GREAT LAKES. The Great Lakes, also called the Inland Seas, consist of five connecting freshwater lakes in east central North America that straddle the international border between Canada and the United States. Collectively they constitute the world's largest body of freshwater, with a surface area of 94,000 square miles (244,000 sq. km) and 5,500 cubic miles (23,000 cu. km) of water. The lakes contain approximately 18 percent of the world's supply of freshwater, with only the polar ice caps having more. From west to east, the lakes are Superior (the largest and deepest of the lakes), Michigan, Huron, Erie (the shallowest), and Ontario (the smallest); they collectively extend about 850 miles (1370 km) west to east and 700 miles (1125 km) from north to south. The Great Lakes form the western portion of the greater St. Lawrence hydrographic system, extending from Minnesota to the Atlantic Ocean.
Lake Superior connects to Huron through Sault Sainte Marie (St. Marys River), and Lake Michigan joins Huron via the Straits of Mackinac. A major inlet north of Lake Huron is Georgian Bay, which lies entirely within Canada. Waters from the three upper Great Lakes (Superior, Michigan, and Huron) flow through the St. Clair River, Lake St. Claire, and the Detroit River into Lake Erie, which in turn is connected to Lake Ontario through the Niagara River and Niagara Falls. The five lakes then drain northeastward into the Atlantic Ocean through the St. Lawrence River. The Great Lakes' drainage basin covers 295,200 square miles (764,570 sq. km) and includes portions of eight states (Minnesota, Wisconsin, Michigan, Illinois, Indiana, Ohio, Pennsylvania, and New York) and the Canadian province of Ontario, which extends along the north shore of four of the lakes. Lake Michigan lies entirely within the boundaries of the United States; the international boundary bisects the other four lakes.
Geologically, the Great Lakes system began to develop three million years ago, during the Precambrian Era, a time of volcanic activity and geological stress that formed major mountain systems that later eroded. Most of central North America was covered by marine seas during the Paleozoic Era, and major continental glaciers advanced over the Great Lakes region beginning about one million years ago. As a result of a series of glacial formations and retreats, glacial deposits and large volumes of meltwater created a basin larger than the present-day Great Lakes. The most recent Great Lakes basin formed between 32,000 and 10,000 years ago; lake levels stabilized about 2,400 years ago. Five biotic provinces are defined on the basis of floral and faunal characteristics, and include Hudsonian to the extreme north, Canadian (Georgian Bay, Lake Nipissing, and the Ottawa River), Carolinian-Canadian Transition (present-day Wisconsin, Michigan, and southern Ontario), Illinoisan (southern Lake Michigan basin), and Carolinian (Ohio, Pennsylvania, and western New York).
Paleo-Indian hunters and gatherers occupied the Great Lakes basin before 9500 b.c.e. and were followed by semisedentary Early Archaic peoples who exploited a wider variety of large and small fauna and diverse flora. More populous and technologically advanced Late Archaic peoples formed small sedentary communities beginning in 3,000 b.c.e. The Archaic-Woodland Transition (1500–100 b.c.e.) was characterized by large sedentary villages, plant domestication, the development of pottery, and cultural adaptations to diverse econiches. The Middle Woodland period (c. 200 b.c.e.–500 c.e.) saw the development of Hopewell culture in Ohio and adjacent states, characterized by circular and serpentine earthworks, enormous artificial mounds, elaborate burial practices, and long-distance trade systems for exotic goods used in burials, such as marine shells from Florida and obsidian from Wyoming. Other areas of the Great Lakes continued an Early Woodland pattern.
The subsequent Late Woodland period (500–1600 c.e.) saw the incursions of peoples and ideas from the Mississippi Valley; an emphasis on the cultivation of maize, beans, squash, and sunflowers; larger populations and settlements; and territorial conflicts between tribes. At European contact a number of major tribes were established in the Great Lakes basin, among them the Ojibwe, Me-nominee, Winnebago, Miami, Potawatomi, Fox, Sauk, Kickapoo, and Mascouten tribes in the upper Great Lakes region, and the Erie, Iroquois (Seneca, Oneida, Cayuga, Onondaga, and Mohawk), and Wenro south of lakes Erie and Ontario, with the Ottawa, Petun, Huron, and Neutral tribes north of those lakes. Miamis, Mascoutens, Mesquakies, and Shawnees occupied the area around Lake Michigan.
The French explorer Jacques Cartier, seeking a northwest passage to the Orient, located the St. Lawrence River during the years of 1534 and 1535. Samuel de Champlain visited lakes Ontario and Huron in 1610, initiating a period of French exploration characterized by missionaries, fur traders, and territorial conflicts between the emerging New France and British colonies along the Atlantic seaboard. The Ottawa River provided a route for Jesuit missionaries and French trappers and traders, who soon visited the upper lakes. Jean Nicolet reached the shores of
|Great Lakes: Physical Features and Population|
|a. Measured at Low Water datum.|
|b. Land drainage area for Lake Huron includes St. Marys River; for Lake Erie includes the St. Clair-Detroit system; for Lake Ontario includes the Niagara River.|
|c. Including islands.|
|d. These totals are greater than the sum of the shoreline length for the lakes because they include the connecting channels (excluding the St. Lawrence River).|
|source: Government of Canada and United States Environmental Protection Agency (1995), 4.|
|Average Deptha (feet)||483||279||195||62||283|
|Maximum Deptha (feet)||1,332||925||750||210||802|
|Volumea (cu mi)||2,900||1,180||850||116||393||5,439|
|Water Area (sq mi)||31,700||22,300||23,000||9,910||7,340||94,250|
|Land Drainage Areab (sq mi)||49,300||45,600||51,700||30,140||24,720||201,460|
|Total Area (sq mi)||81,000||67,900||74,700||40,050||32,060||295,710|
|Shoreline Lengthc (miles)||2,726||1,638||3,827||871||712||10,210d|
|Retention Time (years)||191||99||22||2.6||6|
|Outlet||St. Marys River||Straits of Mackinac||St. Clair River||Niagara River/Welland Canal||St. Lawrence River|
|Population U.S. (1990)||425,548||10,057,026||1,502,687||10,017,530||2,704,284||24,707,075|
Lake Michigan in 1634, and Isaac Jogues and Charles Raymbault ventured to Sault Sainte Marie seven years later. By 1672 the Jesuits had compiled and published an accurate map of Lake Superior. The Iroquois Wars (1641–1701) and a period of French incursion, settlement, and fortifications (1720–1761) followed. By 1673 Louis Jolliet and Jacques Marquette had begun explorations of the upper Mississippi River, followed by Robert Cavelier, Sieur de La Salle, and his expedition (1678–1684). By 1683 a highly accurate map of all the Great Lakes, based on these and other expeditions and journeys, was compiled by Father Louis Hennepin.
Drawn by the fur trade and seeking new lands, English traders from Albany began to explore the upper Great Lakes in the 1690s. To counter this, in 1701 Antoine de la Mothe Cadillac established Fort Pontchartrain du Détroit, which commanded the narrow river between Lake Erie and Lake Huron. It became the focus of French control of the upper lakes and denied access to English traders and exploration. The conflict between the English and French for the control of North America, which centered on the Great Lakes, involved a series of wars and minor conflicts that covered a period of seventy-five years and included participation by Native Americans on both sides. The French and Indian War culminated with the surrender of French Canada to the British in 1760. Pontiac's War (1763–1764) heralded a transitional period with American exploration, migrations, and settlement of the region along the southern shores of the Great Lakes. Notably the Definitive Treaty of Peace signed between Britain and the United States in 1783, ending the Revolutionary War, included an article that called for control of the lakes to be shared between British Canada and the American colonies.
The War of 1812 (1812–1815), between the Americans and the British, also involved Native Americans on both sides in the region of Detroit and the Niagara Frontier. Many of the engagements were fought on and adjoining the Great Lakes. A major naval engagement, the battle of Lake Erie (10 September 1813), was won by the Americans and helped to ensure the sovereignty of the United States through the Treaty of Ghent (1814) and the Rush-Bagot Agreement (1817), which established limitations on naval forces on the Great Lakes.
The promise of agricultural land was a major attraction for immigrants; hence agrarian settlements and fisheries developed on both the American and the Canadian sides of the border during the 1800s. City building, nation building, and industrialization were hallmarks of the nineteenth century as dairying, fruit and vegetable cultivation, logging, and forest exploitation gave way to iron and steel production, papermaking, and chemical manufacture in the twentieth century. The forests around the Great Lakes provided hardwoods and pine, while the Lake Superior region yielded high-quality iron ore and copper. Major agricultural products included corn, wheat, soybeans, grapes, pork, and beef cattle. The industry of the region was, and remains, highly diversified, but significant quantities of iron ore, coal, minerals, grain, and manufactured products are transported throughout the Great Lakes and shipped overseas. Notable transportation improvements included the construction of the Erie Canal, from Albany to Buffalo, New York (completed in 1825); the Canadian Lachine Canal, bypassing rapids in the St. Lawrence River; and the Welland Canal (1829), joining lakes Erie and Ontario. The latter two were surpassed in 1959 by the completion of the St. Lawrence Seaway.
Commercial fishing began about 1820 and peaked between 1889 and 1899 but native fish diminished and have been replaced by introduced species. Sport fishing, water recreation, and cultural tourism have become economically significant in spite of a deterioration in water quality and habitat that accompanied urbanization and industrialization. Pollution, pathogens, eutrophication, toxic contaminants, diminished oxygen levels, the introduction of exotic flora and fauna (such as zebra mussels), and a recent drop in lake water levels are of major concern to inhabitants of the Great Lakes basin.
Perhaps surprisingly, a number of upper Great Lakes cities were founded earlier than many of the settlements situated along the shores of the lower lakes. In the main lakes the early settlements were fur trading posts, such as Green Bay in modern Wisconsin at the mouth of the Fox River, established in 1634 and with a population of more than 103,000 by 2000. Other posts were established at Chicago in 1673; at Thunder Bay, Ontario, in 1678; and at Duluth, Minnesota, in 1692. In the lower lakes Hamilton, Ontario, was established in 1669 and by 2000 was an industrial center with 320,000 inhabitants; Buffalo, New York, a former Seneca Indian village settled by Europeans in 1679, was by 2000 an industrial city with more than 300,000 inhabitants. Detroit, settled in 1701, has become a center of automotive production and has a population exceeding 1,045,000 in 2000. Established in 1720, Toronto, now the capital of the province of Ontario and a financial and commercial center, had a 2000 census of 640,000. Because explorers, missionaries, and travelers could bypass Lake Erie by venturing from Lake Ontario and the Ontario River to the upper lakes, settlements along Lake Erie were founded late in the region's history. These include Erie, Pennsylvania, in 1753 (in 2000 an industrial and agricultural community of 105,000); Cleveland, Ohio, in 1786 (a major center of heavy industry with a population exceeding 506,000 in 2000); London, Ontario, in 1792 (by 2000 an industrial and agricultural center with more than 303,000 persons); and Toledo, Ohio, in 1794 (another industrial community, with 323,000 persons in 2000). Rochester, New York, now a center for imaging science, was founded on the Genessee River, which flows into Lake Ontario, in 1789; Milwaukee, Wisconsin, situated at the mouth of the river of the same name, was founded in 1800 and was a major center of the brewing industry. In 2000 Rochester had a population of 217,000, and Milwaukee's census exceeded 617,000. Chicago grew from a trading post to become a leading rail and lake transport hub, as well as an industrial and commercial center with a population of 2,840,000 in 2000.
Ashworth, William. Great Lakes Journey: A New Look at America's Fresh-water Coast. Detroit: Wayne State University Press, 2000.
Bogue, Margaret B. Around the Shores of Lake Superior: A Guide to Historic Sites. Madison: University of Wisconsin Press, 1979.
———. Fishing the Great Lakes: An Environmental History, 1783–1933. Madison: University of Wisconsin Press, 2000.
Burns, Noel M. Erie: The Lake That Survived. Totowa, N.J.: Rowman & Allanheld, 1985.
———. The Great Lakes Guidebook: Lakes Ontario and Erie. Ann Arbor: University of Michigan Press, 1985.
Gentilcore, R. Louis, ed. Historical Atlas of Canada, vol. 2 : The Land Transformed, 1800–1891. Toronto: University of Toronto Press, 1990.
Government of Canada and United States Environmental Protection Agency. Great Lakes Factsheet No. 1. In The Great Lakes: An Environmental Atlas and Resource Book, 3d ed., 1995. Available from http://www.epa.gov/glnpo/atlas/fact1txt.html.
Harris, R. Cole, ed. Historical Atlas of Canada, vol. 1 : From the Beginning to 1800. Toronto: University of Toronto Press, 1987.
Hatcher, Harlan H. The Great Lakes. London and New York: Oxford University Press, 1944.
———. Lake Erie. Indianapolis and New York: Bobbs-Merrill, 1945. Reprinted Westport, Conn: Greenwood, 1971.
Hatcher, Harlan H., and Erich A. Walter. Pictorial History of the Great Lakes. New York: Crown, 1963.
Hough, Jack L. Geology of the Great Lakes. Urbana: University of Illinois Press, 1958.
Karpinski, Louis C. Maps of Famous Cartographers Depicting North America: An Historical Atlas of the Great Lakes and Michigan, 2d ed. Amsterdam: Meridian, 1977. First published 1880.
Kerr, Donald, ed. Historical Atlas of Canada, vol. 3 : Addressing the Twentieth Century, 1891–1961. Toronto: University of Toronto Press, 1993.
Kuchenberg, Tom. Reflections in a Tarnished Mirror: The Use and Abuse of the Great Lakes. Sturgeon Bay, Wis.: Golden Glow, 1978.
Landon, Fred. Lake Huron. New York: Russell & Russell, 1972. First published 1944.
Ludwigson, John O. Two Nations, One Lake: Science in Support of Great Lakes Management. Ottawa: Canadian National Committee for International Hydrological Decade, 1974.
Mason, Ronald J. Great Lakes Archaeology. New York: Academic Press, 1981.
McGucken, William. Lake Erie Rehabilitated: Controlling Cultural Eutrophication, 1960s–1990s. Akron, Ohio: University of Akron Press, 2000.
Office of the Great Lakes. Great Lakes Trends: Into the New Millennium. Lansing: Michigan Department of Environmental Quality, 2000.
Pound, Arthur. Lake Ontario. Port Washington, N.Y.: Kennikat Press, 1970.
Skaggs, David C. A Signal Victory: The Lake Erie Campaign. 1812–1813. Annapolis, Md.: Naval Institute Press. 1997.
St. John, John R. A True Description of the Lake Superior Country. Grand Rapids, Mich.: Black Letter-Press, 1976.
Tanner, Helen H., ed. Atlas of Great Lakes Indian History. Norman: University of Oklahoma Press for The Newberry Library, 1987.
Thompson, Mark L. Graveyard of the Lakes. Detroit: Wayne State University Press, 2000.
Thwaites, Reuben Gold. The Jesuit Relations and Allied Documents. 73 vols. Cleveland: Burrows Brothers, 1896–1901.
Charles C. Kolb
See also Explorations and Expeditions: French ; Michigan, Upper Peninsula of ; Tribes .
Located in north-central North America, the Great Lakes are five large fresh-water lakes interconnected by natural and artificial waterways: Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario. Carved by ancient glaciers, these lakes contain approximately 20 percent of the world's surface fresh-water supply and 95 percent of the surface fresh water in the United States. The Great Lakes waterbody is so large that its natural features can be seen from the Moon.
Great Lakes Watershed
Native Americans were the original inhabitants of the Great Lakes basin. Historically, the Great Lakes played a significant role in Native American societies and approximately 120 bands of native peoples have occupied this region over the course of history. Notable tribes inhabiting the Great Lakes region include the Chippewa, Fox, Huron, Iroquois, Ottawa, Potawatomi, and Sioux. These Native peoples played an instrumental role when European explorers came to the region in the early 1600s, particularly in the development of the fur trade. Each of the names of the Great Lakes comes from either a Native tribe name or the Native words for the lakes.
Straddling the U.S.–Canada boundary, today's Great Lakes watershed is home to approximately 40 million Americans and Canadians. This population represents about 10 percent of the U.S. population and 25 percent of the Canadian population. In the United States, four of the twelve largest cities are located on the shores of the Great Lakes. The lakes constitute the largest inland water transportation system in the world, and have played an important role in the economic development of both the United States and Canada.
The Great Lakes encompass 16,000 kilometers (10,000 miles) of inland coastal waters, and collectively have been referred to as "the inland seas" and "the fourth coast of the United States". Lake Michigan is located entirely within the United States, while the other four lakes form a partial border between the United States and Canada. The lakes are bordered by the Canadian province of Ontario and by the eight U.S. states of Minnesota, Wisconsin, Illinois, Michigan, Indiana, Ohio, Pennsylvania, and New York. The westernmost point of the Great Lakes is near Duluth, Minnesota, and the easternmost point is just north of Syracuse, New York (and connects with the St. Lawrence Seaway).
Covering a total surface area of about 244,000 square kilometers (94,000 square miles) the Great Lakes contain a volume of approximately 23,000 cubic kilometers (5,500 cubic miles) of water. This tremendous volume is hard to conceptualize, but if it were spread over the contiguous 48 states, its waters would average about 2.9 meters (9.5 feet) deep. Together the lakes drain about 750,000 square kilometers (about 290,000 square miles), with the primary outlet being the St. Lawrence River.
The shores of the Great Lakes vary considerably from region to region. On the eastern side of Lake Michigan, sandy beaches are prevalent, whereas the shores of Lakes Superior and Huron are primarily rocky, and often framed by cliffs comprised of sandstone and shale. Wetlands are found along Lake Ontario's shore, including Canada's well-known Point Pelee National Park. These shoreline systems serve to protect their inland areas by absorbing the force of wind and wave energy from the lakes.
The Great Lakes and surrounding area is a natural resource of great importance in North America. The region also serves as the focal point of the industrial and agricultural base of the Midwest's heartland by providing a strong marine transportation system. Rivers, straits, canals, locks, and channels interconnect the Great Lakes, and together form one of the busiest shipping arteries in the world.*
With the 1959 completion of the St. Lawrence Seaway, the commercial potential of the lakes increased because they could now accommodate medium-sized oceangoing vessels. In fact, the St. Lawrence Seaway brought several Great Lakes ports closer to European markets than existing East Coast or Gulf ports, saving shippers both time and money. For example, the shipping distance from the port city of Baltimore, Maryland, to Liverpool, England, is 6,334 kilometers (3,936 miles). With the addition of the St. Lawrence Seaway, ships could reach Detroit, Michigan by covering only 5,911 kilometers (3,673 miles).
The Great Lakes today are home to the U.S. and Canadian flag fleets and to dozens of international vessels from ports around the world. The movement of shipping cargo is estimated to provide approximately 60,000 jobs throughout the Great Lakes region. The ability to efficiently ship materials such as iron ore, coal, and limestone enabled the rise of the steel and automobile industries in the Great Lakes region.
Recreation in the Great Lakes area became important beginning in the nineteenth century. A thriving pleasure-boat industry based on newly constructed canals on the lakes brought vacationers into the region, as did the already established railroads and highways. The lower lakes wilderness region attracted people who were seeking health benefits and even miracle cures from mineral waters.
In the twentieth century, the U.S. and Canadian governments acquired border lands to develop a system of parks, wilderness areas, and conservation areas in order to protect valuable resources and to serve the recreational needs of the population. Unfortunately, by the time the need for publicly accessible recreation lands had become apparent, much of the land, including nearly all the shoreline on the lower lakes, was privately held. Today, about 80 percent of the U.S. shoreline and 20 percent of the Canadian shore is privately owned.
Niagara Falls was one of the first Great Lakes tourist attractions, and it remains a popular destination. Niagara Falls were formed approximately 10,000 years ago when retreating glaciers exposed the Niagara escarpment, allowing the waters of Lake Erie to flow north to Lake Ontario. Until the early 1950s, the falls eroded at an average rate of 1 meter (3 feet) per year, but human modifications to the river's flow have since reduced the rate of erosion. Today, Goat Island splits the rapids into the American Falls (51 meters or 167 feet high and 323 meters or 1,060 feet wide) and the Horseshoe, or Canadian, Falls (48 meters and 158 feet high and 792 meters or 2,600 feet wide).
Great Lakes Fisheries
The Great Lakes support diverse fresh-water fisheries. Fish were a primary source of food to Native tribes of the Great Lakes region, and settlements often were established at places where the fisheries were good. Sturgeon, lake trout, and whitefish were popular catches of their time. Birchbark canoes and nets made from willow bark were commonly used to harvest fish. Tribal fishermen also practiced ice fishing, spearing through the ice and fishing with hand-carved decoys. Fish also were an important source of food to the early European settlers.
Commercial fishing began around 1820, and annual catches grew approximately 20 percent per year as improved fishing technologies were applied. During the 1880s, some species in Lake Erie began to decline. Commercial fishing harvests from the Great Lakes peaked between 1889 and 1899 at around 67,000 metric tons (147 million pounds).
By the late 1950s, the golden days of the Great Lakes commercial fishery were over. Since that time, average annual catches have been approximately 50,000 metric tons (110 million pounds). The fishery is increasingly dominated by smaller and relatively lower valued species. Moreover, the fishery is a mix of native and introduced species, with a number of species being restocked regularly. While each of the Great Lakes has its own mainstay species, common catches currently include lake trout, salmon, walleye, perch, whitefish, smallmouth bass, steelhead, and brown trout.*
In the 100 years since its peak harvests, the Great Lakes fishery has been severely threatened, mainly due to the effects of overfishing, shoreline and stream habitat destruction, and pollution. The accidental and deliberate introductions of nonnative invasive species, such as the sea lamprey and zebra mussel, have also played a role in the decline of this fishery. Today, only isolated pockets of the once large commercial fishery remain, and even these are uncertain, due largely to contaminants . Efforts undertaken to stabilize the commercial fishery have maintained its commercial and sport value at more than $4 billion annually as of 2002.
The degradation of the Great Lakes can be traced back to the westward expansion of the North American population. The fishery decline in late 1800s was one of the region's earliest environmental problems. Agricultural and forestry practices resulted in siltation, increased water temperature, and loss of habitat for native fish species. The discharge of pollutants into the lakes accompanied the region's population growth. The vastness of the Great Lakes encouraged the mistaken belief that their great volumes of water could indefinitely dilute pollutants to harmless levels.
Yet impacts to the environment and human health were inevitable. The direct discharge of domestic wastes from cities along the lakeshores led to typhoid and cholera epidemics in the early 1900s. Moreover, fish would become so contaminated by municipal and industrial pollutants that their flesh was no longer safe to eat.
In 1909, the United States and Canada cooperatively negotiated the Boundary Waters Treaty. This treaty established the International Joint Commission (IJC) which is a permanent binational body addressing, among other important boundary issues, water quality concerns and the regulation of water levels and flows between the two countries. The Great Lakes Water Quality Board and the Great Lakes Science Advisory Board are bodies of the IJC. Six commissioners are the final arbitrators of the IJC: the United States and Canada appoint three each.
Several key water agreements have been produced by the International Joint Commission process, most notably the 1972 and 1978 Great Lakes Water Quality Agreements. Since the 1972 agreement, forty-three Areas of Concern (AOC) have been identified, twenty-six located within the United States, twelve located within Canada, and five that are shared by both countries.
Primarily due to the declining condition of Lake Erie, the 1978 Agreement went beyond setting narrow water-quality goals and addressed toxic contamination from an ecosystem perspective. This 1978 agreement has become a driver of the ecosystem approach to water management throughout the Great Lakes basin, and further amendments were passed in 1987. The 1987 U.S. Clean Water Act (Section 118) also addressed the Great Lakes situation and included provisions for monitoring of their water quality.
The Story of Lake Erie.
Reports since the 1950s of the "death" of Lake Erie serve as a reminder of the human impact on natural ecosystems. In the 1950s and 1960s, the Cuyahoga River, which empties into Lake Erie, caught fire due to oily pollutants on its surface.* Pollution problems from organic and inorganic wastes and nutrients were compounded by the effects of deforestation, sedimentation, and wetland drainage. Floating raw sewage, algal blooms, and the buildup of toxic metals in its sediments caused beach closings, oxygen depletion, contaminated fish advisories, and reports of the lake's death. Many feared the other lakes would follow a similar demise.
Concerted management efforts were undertaken in the 1970s to restore Lake Erie and the other lakes back to health. Yet after more than two decades of mostly good news about the lake's improving health, Lake Erie again is showing signs of an environmental crisis. Scientists attribute diverse and complex causes to the latest ecosystem disruption: large-scale fish and bird die-offs; a large "dead zone" off the Ohio shoreline; and the threat of invasion by more nonnative species, particularly the Asian carp and quagga mussel.
Renewed Concerns Over Water Levels
Measurements of water levels in the great Lakes constitute one of the longest continuous hydrometeorological datasets in North America. Reference gage records start in 1860, with sporadic records going back to the early 1800s.
Water levels on the Great Lakes change seasonally each year and can vary dramatically over longer periods. Seasonally, changes are to be expected, and the range of seasonal water-level fluctuation averages about 0.3 to 0.45 meters (12 to 18 inches) from winter lows to summer highs. Long-term fluctuations are harder to predict, and occur over periods of consecutive years. Over the last century, the range from extreme high to extreme low water levels has been nearly 1.2 meters (4 feet) for Lake Superior, and between 1.8 and 2.1 meters (6 to 7 feet) for the other Great Lakes.
As of 2002, the Great Lakes apparently were starting to recover from water-level lows not recorded since the mid-1960s. The declines probably were due predominantly to evaporation during the warmer-than-usual temperatures experienced during the late 1990s, a series of mild winters, and the below-average snowpack melts in the Lake Superior basin. Lower water levels have a variety of effects, including affecting shipping, recreation, property values, and habitat diversity. Concerns relating to potential impacts of global climate change on the Great Lakes are being researched.
Diversion of Great Lakes Waters
Proposals to divert water from the Great Lakes hydrologic system have proven very controversial. As these lakes are a shared international resource, many governments and organizations are concerned with managing and protecting the integrity of the Great Lakes waters and ecosystem. For these groups, the bulk export of Great Lakes basin water is an increasing concern in a water-scarce world.
Existing diversions comprising sizable quantities of water involve Ontario, Canada; Chicago, Illinois; and the intrabasin transfers of the Welland Canal. These diversions have been operational since the early 1900s. Much smaller diversions involve New York, Wisconsin, Ohio (via the City of Akron), and Michigan (via the City of Detroit).
Since 1995, new diversion and export schemes have included:
- a permit granted to Perrier to bottle water from an aquifer in Michigan;
- a plan to divert millions of liters of groundwater per day from Lake Michigan's watershed for use in mining-related activities that would discharge much of the diverted water into the Mississippi River Basin;
- a permit issued by the Canadian province of Ontario for the bulk transfer of water from Lake Superior for sale in Asian markets as bottled water (but this permit was later revoked); and
- a 2002 proposal by the City of Detroit to bottle and sell water from the Detroit River.
Water diversions and exports have come under intense scrutiny, especially as the lake levels were falling and reached near-record lows. As levels rise, many see opportunities to use the waters of the Great Lakes for commercial uses and to make profits. A debate also has intensified over whether groundwater is part of "Great Lakes waters" as defined by the Water Resources Development Act of 1986.
Two policies have been enacted to attempt to govern potential diversions from the Great Lakes basin: the Boundary Waters Treaty of 1909 and the Great Lakes Charter of 1985. The Boundary Waters Treaty expresses a commitment by both countries to refrain from harming the waters of the other country (e.g., due to bulk exports). The Great Lakes Charter specifically urges U.S. governors and Canadian premiers in the region to seek each other's approval prior to granting diversion requests for large-volume bulk exports above a threshold level; however, this is a nonbinding treaty.
Additionally, U.S. diversions from the Great Lakes may also be subject to the Water Resources Development Act of 1986 (amended in 2000). This act requires the approval by all eight U.S. Great Lakes governors on any proposed exports out of the basin. Within the region, many are concerned that this policy is not strong enough to protect the lakes from diversions and several pieces of legislation have been introduced into Congress to help prevent future diversions and even to create a moratorium on these bulk exports.
While efforts to protect Great Lakes waters surely will continue, international free trade agreements may clear the path for additional diversions, bulk removals, or the selling of bottled water. On the other hand, ongoing concerns over impacts on lake levels and potential consequences from climate change may spur new laws and treaties to prevent future diversions and exports from the basin.
Future of the Great Lakes
Managing the Great Lakes system and implementing an ecosystem approach are made difficult by the myriad of agencies and programs with responsibility in this area. Two countries, eight states, two provinces, and numerous tribal councils and local jurisdictions share an interest in managing the waters of the Great Lakes. Many local citizens groups have also formed to address water issues.
A 2002 report by the International Joint Commission concluded that progress to restore and maintain the chemical and biological integrity of the waters of the Great Lakes basin ecosystem is making some progress, but proceeding at a slow pace. It also stated that cleaning up contaminated sediments and stopping the invasion of alien species are two top priorities for restoring the chemical and biological integrity of this ecosystem. The Great Lakes basin has and will continue to serve as a vast laboratory where scientists can learn more about both ecosystem and water management.
see also Algal Blooms in Fresh Water; Canals; Clean Water Act; Economic Development; Environmental Movement: Role of Water in the; Fisheries, Fresh-Water; International Cooperation; Lake Management Issues; Pollution by Invasive Species; Pollution of Lakes and Streams; Pollution Sources: Point and Nonpoint; Ports and Harbors; Recreation; Tourism; Transboundary Water Treaties; Transportation.
and William Arthur Atkins
Ashworth, William. Great Lakes Journey: A New Look at America's Freshwater Coast. Detroit, MI: Wayne State University Press, 2000.
MacKenzie, Susan Hill. Integrated Resource Management: The Ecosystem Approach in the Great Lakes Basin. Washington, D.C.: Island Press, 1996.
Great Lakes Commission. <http://www.glc.org/>.
Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration. <http://www.glerl.noaa.gov/>.
Great Lakes Fishery Commission. <http://www.glfc.org>.
Great Lakes Information Network. <http://www.great-lakes.net/>.
International Joint Commission. <http://www.ijc.org>.
LAKE SUPERIOR IS APTLY NAMED
Lake Superior is the largest lake with respect to both surface area and volume of water. It is also the deepest and coldest of the five lakes. If filled with the smaller lakes, Lake Superior could contain each of the other four Great Lakes and three more lakes the size of Lake Erie. The northwestern section of Lake Superior contains the archipelago of Isle Royale National Park.
* See "Army Corps of Engineers, U.S." for a photograph of a vessel at the Soo Locks.
* See "Fisheries, Fresh-Water" for a photograph of a recreational fisher holding a Lake Michigan steelhead.
* See "Environmental Movement, Role of Water in the" for a photograph of the 1952 Cuyahoga River fire.
The five Great Lakes—Erie, Huron, Michigan, Ontario, and Superior—are environmentally unique and invaluable to the United States and Canada. Together, the lakes extend over 750 mi (1,200 km) from east to west, comprising 18% of Earth's freshwater (its largest single source) and 95% of North America's freshwater, dominating the eight states and two Canadian provinces that border them. The lakes' influence on transportation, industry, and agriculture in this area is pervasive, and over a quarter of the population of Canada and one tenth of the United States population live in the Great Lakes watershed.
As the issue of global warming gains widespread acceptance, its effects on the Great Lakes and the surrounding region have become better documented and of more immediate concern to scientists, policymakers, and concerned members of the public. All need access to information on how further regional changes may affect specific aspects of life in the Great Lakes area—including potentially drastic shifts in economy, ecology, and public health—in order to make decisions that will help alleviate the changes or to better adapt to them.
Historical Background and Scientific Foundations
The United States Global Change Research Program (USGCRP) initiated its national assessment of the consequences of climate change in 1997, and the Great Lakes Regional Assessment Group issued its report, Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change in the Great Lakes Region in 2000, with contributions from over thirty specialists in different fields. Researchers have continued to build on this assessment, determining the probable impacts of climate change on Great Lakes communities and ecosystems.
The Great Lakes and surrounding region already suffer from serious air and water pollution, burgeoning populations of invasive species, and continued habitat loss. It is likely that ongoing climate change will intensify current problems as well as create new ones.
Impacts and Issues
In general, temperatures are expected to warm in the Great Lakes area, ranging from 5-12°F (3-6°C) warmer in winter, and anywhere from 5-20°F (3-11°C) warmer in summer. This would greatly reduce the length of winter and the time that lakes (including numerous smaller inland lakes) are covered with ice. Great Lakes water levels may decline anywhere from 2 to 8 ft (0.6 to 2.4 m) despite modest increases in rainfall, mainly because of the increase in evapotranspiration associated with the loss of winter ice cover and warmer temperatures. Lower lake levels will have major impacts on shipping, hydroelectric power, and water use. Water shortages and conflicts over supply are expected to increase.
Hotter summer temperatures will increase the duration of summer stratification (seasonal changes in temperature and density) in all lakes, and according to Peter Sousounis and Patty Glick (2000), “will reduce the seasonal mixing that replenishes critical oxygen to biologically productive lake zones, possibly shrinking lake biomass productivity by around 20%. This will include losses of zooplankton and phytoplankton that form the very base of aquatic food chains, and are critical to the survival of the many species of fish that live in the Great Lakes.” An associated increase in the number of dead zones (areas without living organisms), especially in the deeper portions of Lakes Superior, Michigan, and Huron, is likely.
Instances of extreme heat and rain, producing increased river flooding, agricultural runoff, and sewage overflows, will likely become more common in the summer months. Lake-effect snow may become heavier or more frequent in areas already prone to it. There is evidence that high lake-effect snowfall rates in the twentieth century already reflect warmer lake temperatures.
Associated effects on Great Lakes ecosystems may be profound. Distributions of many species are expected to shift north (or out of the lakes altogether) as temperatures warm, wetlands dry up, and the shoreline breeding grounds that are important for fish, migratory birds, and amphibians suffer. Forest composition is also predicted to change, and many of the invasive plant, insect, and fish species currently found in regions to the south of the Great Lakes may further stress native species. Hotter and drier summer conditions will also promote more frequent wildfires, especially in northern forested areas.
Although earlier studies predicted that agriculture in the area would not be seriously disrupted, new studies show that the increased variability in rainfall now predicted (more rain, but less evenly spread out) may be very detrimental, especially to corn and soybeans.
The anticipated effects of climate change on human health are significant, if not as grave as in some other regions. Asthma and other respiratory diseases may be exacerbated by high ground-level ozone levels and the increased air pollution that accompanies heat waves. A higher risk of waterborne infectious diseases and diseases carried by ticks and mosquitoes is also predicted.
WORDS TO KNOW
BIOMASS: The sum total of living and once-living matter contained within a given geographic area. Plant and animal materials that are used as fuel sources.
EVAPOTRANSPIRATION: Transfer of water to the atmosphere from an area of land, combining water transfer from foliage (transpiration) and evaporation from non-living surfaces such as soils and bodies of water.
LAKE-EFFECT SNOW: Snow that falls downwind of a large lake. Cold air moving over relatively warm lake water is warmed and moistened; after leaving the lake, the air cools again and some of its moisture precipitates out as snow.
PHYTOPLANKTON: Microscopic marine organisms (mostly algae and diatoms) that are responsible for most of the photosynthetic activity in the oceans.
STRATIFICATION AND TURNOVER: Two processes in lakes that have to do with the mixing of waters at different depths. Stratification is layering, which occurs when upper layers are warmer and float stably on the deeper water. Stratification opposes mixing or turnover, which is the exchange of water (and thus of dissolved chemicals and suspended particles) between deep and surface waters.
ZOOPLANKTON: Animal plankton. Small herbivores that float or drift near the surface of aquatic systems and that feed on plant plankton (phytoplankton and nanoplankton).
Finally, tourism and local recreation—which are significant to local economies and the sense of place that defines the region—are likely to change as the lakes themselves and the landscapes around them alter. Although this aspect of change is harder to predict than fish resources or forest composition, it is still of great concern to the 60 million inhabitants who live in the Great Lakes region.
See Also Agriculture: Vulnerability to Climate Change; Biodiversity; Blizzards; Economics of Climate Change; Fisheries; Hydrologic Cycle; Lake Effect Snows; North America: Climate Change Impacts; Water Shortages.
Dempsey, Dave. On the Brink: The Great Lakes in the 21st Century. East Lansing, MI: Michigan State University Press, 2004.
Great Lakes Regional Assessment Group for the U.S. Global Change Research Program. Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change in the Great Lakes Region. Ann Arbor, MI: University of Michigan, Department of Atmospheric, Oceanic and Space Sciences, 2000.
Kling, George W., Katharine Hayhoe, L. B. Johnson, et al. Confronting Climate Change in the Great Lakes Region: Impacts on Our Communities and Ecosystems. Cambridge, MA: Union of Concerned Scientists and Ecological Society of America, 2003.
Burnett, Adam W., Matthew E. Kirby, et al. “Increasing Great Lake-Effect Snowfall During the Twentieth Century: A Regional Response to Global Warming?” Journal of Climate 16, 21 (2003): 3535-3542.
Oakes, Larry. “Lake Superior Called ‘Early Victim of Climate Change.’” Minneapolis Star Tribune (October 30, 2007).
Santos, Fernanda. “Inch by Inch, Great Lakes Shrink, and Cargo Carriers Face Losses.” The New York Times (October 22, 2007).
Scheraga, J. D., and J. Furlow. “Preface to the Potential Impacts of Climate Change in the Great Lakes Region.” Journal of Great Lakes Research 28 (2002): 493-495.
“Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change, Overview: Midwest.” U.S. Global Change Research Program, October 12, 2003. < http://www.usgcrp.gov/usgcrp/Library/nationalassessment/overviewmidwest.htm> (accessed November 14, 2007).
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Sousounis, Peter, and Patty Glick. “The Potential Impacts of Global Warming on the Great Lakes Region: Critical Findings for the Great Lakes Region from the First National Assessment of the Potential Consequences of Climate Variability and Change,” 2000. < http://www.climatehotmap.org/impacts/greatlakes.html> (accessed November 14, 2007).
Sandra L. Dunavan
The Great Lakes are a system of five large freshwater lakes in central North America—Lake Erie, Lake Huron, Lake Michigan, Lake Ontario, and Lake Superior—that drain into the Atlantic Ocean via the St. Lawrence Seaway. Combined, the Great Lakes constitute the largest surface area of unfrozen fresh water in the world: 94,850 mi2 (245,660 km2), an area larger than the United Kingdom. Except for Lake Michigan, which is wholly contained in the United States, the Great Lakes form a natural segment of the U.S.-Canadian border.
Lake Superior is the largest of the five lakes by almost 10,000 mi2 (41,682 km2), and has the greatest average (and maximum) depth. As a result, Lake Superior contains slightly more water than all the other Great Lakes combined—almost 3,000 mi3 (12,504 km3). The deepest parts of all the Great Lakes except Lake Erie are below sea level; in Lake Superior's case, over 600 ft (183 m) below.
Lake Superior has an average depth of 487 ft (148 m), a maximum depth of 1,302 ft (397 m) and covers 31,820 mi2(82,413 km2). Lake Huron has an average depth of 195 ft (59m), a maximum depth of 750 ft (229 m), and covers 23,010 mi2 (59,596 km2). Lake Michigan, covering 22,400 mi2(58,016 km2), has an average depth of 276 ft (84 m), and a maximum depth of 923 ft (281 m). Lake Erie has an average depth of 62 ft (19 m), a maximum depth of 210 ft (64 m), and covers approximately 9,930 mi2 (25,719 km2). Lake Ontario, the smallest of the Great Lakes in terms of surface area (7,520 mi2/19,477 km2), has an average depth of 62 ft (19 m) but reaches a maximum depth of 778 ft (237 m).
The Great Lakes drain 295,800 mi2 (766,118 km2) of watershed (counting the surfaces of lakes themselves), or about 3% of the continent. Half the water entering the lakes evaporates; the rest flows from lake to lake, west to east, until it reaches Lake Ontario and then the St. Lawrence River.
By geological standards, the Great Lakes formed very recently. Prior to the beginning of the ice ages of the Pleistocene Epoch—about 1 million years ago—river valleys drained through the areas now occupied by the five lakes. As the ice-sheets flowed southward they favored these preexisting channels, scouring them and so increasing their depth. The latest glacial episode was the Wisconsin Glaciation , which ended about 18,000 years ago. When melting removed the glacier's enormous weight, the land began to rise. (It is still rising, at about .12 in / 3 mm per year.) This rising of the land, along with deposition of glacial sediments (moraines ), blocked all drainage from the Great Lakes area except eastward via the St. Lawrence. Lake Superior is the only Great Lake not formed by glacial scouring and deposition of moraines. Lake Superior's basin, although somewhat enlarged by glacial scouring, is the trough of a V-shaped fold in the rock termed a syncline .
But the Wisconsin glaciation did not simply advance to a most southerly limit, then retreat in an orderly way. It advanced and retreated several times over thousands of years in a three-steps-northward, two-steps-southward fashion. These oscillations partially uncovered and recovered the Great Lakes basins, forming a series of lakes corresponding partly to the modern ones. At one point, a superlake submerged what are today the basins of Superior, Michigan, and Huron. The history of these fluctuations can be traced primarily by the many abandoned beaches that are today found far above water level (often hundreds of feet above). Each abandoned beach records a lake stage or period during which the water level was stable long enough to form a beach. From these and other data, it is known that Erie reached its present level about 10,000 years ago; Ontario about 7,000 years ago; and Superior, Michigan, and Huron only about 3,000 years ago.
Human activity has significantly altered the chemistry and ecology of the lower four lakes, which are ringed by such cities as Buffalo, Chicago, Cleveland, Detroit, Gary, Milwaukee, Rochester, Toledo, and Toronto. Sewage and industrial effluents have burdened these lakes increasingly for over a century. (Chicago and several other cities, however, now divert their sewage southward, away from the lakes.) Lake Superior has been less affected by pollution, having no major settlements on its shores.
Another detrimental side-effect of human activity is the introduction into the lake ecosystem, both deliberate and accidental, of non-native species. The sea lamprey (1930s), alewife (probably 1940s), and zebra mussel (1980s) have been particularly destructive to the native lake fauna. Alewives are now the most abundant fish species in the lakes. They suffer intermittent mass die-offs, wash up on the beaches by the millions, and must be removed using bulldozers and trucked away.
See also Drainage basins and drainage patterns; Glacial land-forms; Syncline and anticline; Water pollution and biological purification
The advance and retreat of glaciers over millions of years scraped and scoured the Great Lakes basins until they attained their present form about 10,000 years ago. Forming the largest system of inland lakes in the world, the Great Lakes have a surface area of 94,200 mi2 (244,000 km2) and a volume of more than 28 trillion yd4 (22,000 km3) of water, 20 percent of the world's surface freshwater.
Lake Superior, with more than 31,660 mi2 (82,000 km2) of water, has the largest surface area of freshwater on earth. Lake Huron, the world's fifth largest lake, is at the same elevation and about the same size as Lake Michigan, the world's sixth largest lake. The two are joined by the narrow, deep Straits of Mackinac. Their accumulated waters empty into the St. Clair River which flows into the 460 mi2(1,190 km2) Lake St. Clair. The water continues its flow into the Detroit River before entering Lake Erie , the eleventh largest lake in the world. It is the oldest, shallowest, busiest, and most eutrophic of the Great Lakes. The waterway continues on into the Niagara River, then to the famous Niagara Falls, where the water descends a total of 325 ft (99 m) before it empties into the last Great Lake, Ontario. The fourteenth largest lake on earth, Lake Ontario is the smallest in surface area but the second deepest of the Great Lakes. It discharges into the St. Lawrence River, which flows into the Atlantic Ocean at the Gulf of St. Lawrence.
The first European explorers discovered a great variety of native fish. Approximately 153 species were eventually identified before human interference disrupted the ecosystem , first by overfishing , and then by lumbering and industrial development. As many species of fish have disappeared, about twenty new species have been introduced. Some, such as the Pacific salmonids, carp, and smelt, were introduced intentionally. Others, such as the sea lamprey, alewife, and zebra mussel , gained access through the Erie and Welland Canals or by release with the ballast water of vessels transporting other cargo.
Today, lake trout, burbot, and whitefish are the principal catches of a once extraordinarily rich fisheries enterprise. Despite the decline in the quality and numbers of suitable fish, sport and commercial fishing are still vital Great Lakes industries. The sport fishery consists primarily of coho, chinook salmon , steelhead trout, walleye, and perch. They now attract about five million anglers annually with a regional economic benefit of about $2 billion.
Besides directly water-related activities, presently, one-fifth of the industry and commerce of the United States is located in the Great Lakes catchment basin because of the availability of abundant cheap and clean freshwater and accessible, efficient water transportation among the lakes and to the oceans. As a consequence, pollution has taken some obvious as well as more subtle forms. Using the lakes as a cheap sewage disposal site for shoreline city populations began in the early seventeenth and eighteenth centuries and continued until the early 1970s. To improve the quality of the Great Lakes, the first efforts concentrated on preventing or removing conventional pollutants such as phosphates , suspended solids, and nitrogen .
More deadly toxic contaminants often are not visible and so initially attracted less attention. Over the past fifty years municipal and industrial wastes so polluted the waters, especially the lower Great Lakes, that, beginning in the middle 1960s organochlorides were identified as serious contaminants. Fish were collecting, through bioaccumulation , relatively large concentrations of agricultural pesticides such as DDT and dieldrin as well as the industrial chemical polychlorinated biphenyl (PCB) in their tissues. These were passed into the human food chain/web . By 1980 more than 400 organic and heavy metals contaminants had been found in fish, and fishermen were warned to limit their consumption. The effects of pollutants are seen primarily at the tops of food chains and are usually discovered through changes in population levels of predator species. Organochlorines and methylated mercury , for example, bioaccumulate to levels that may cause reproductive failures in fish-eating birds and animals such as cormorants, eagles, and mink.
Between 1969 and 1972 legislation was enacted in several states bordering the Great Lakes basin to restrict or ban the use of dieldrin, DDT, PCBs, mercury and other toxic chemicals . After point source discharges were regulated, lake trout and chub, especially in Lake Michigan, showed dramatic declines in these contaminants. By 1978–79, however, the fish contaminant declines were only slight; or the levels remained relatively constant, reflecting airborne inputs as well as the remobilization of contaminants from the sediment .
This problem is likely to continue because the turnover rates of the Great Lakes are very slow; and mercury, PCBs and the pesticides DDT, dieldrin and chlordane are very resistant to degradation in the environment . Also, these compounds continue to enter the Great Lakes ecosystem from highly diffuse nonpoint sources such as airborne deposition, agricultural and urban runoff , remobilization from the sediments, leaching from municipal and industrial landfills, municipal and industrial discharges, and illegal dumping.
[Frank M. D'Itri ]
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Hough, J. L. Geology of the Great Lakes. Urbana, IL: University of Illinois Press, 1958.
Sixth Biennial Report on Great Lakes Water Quality. Windsor, Ont.: International Joint Commission, 1992.
Weller, P. Fresh Water Seas: Saving the Great Lakes, Between the Lines. Toronto: Publishers, 1990.