St. Lawrence Seaway

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St. Lawrence Seaway

The St. Lawrence Seaway is a series of canals, locks, and lakes giving ocean-going ships of the Atlantic access to the Great Lakes and dozens of inland ports, including Toronto, Cleveland, Chicago, and Duluth. A herculean engineering project built jointly by the Canadian and United States governments, the St. Lawrence Seaway has become an essential trade outlet for the Midwest. It has also become an inlet for exotic and often harmful aquatic plants and animals, from which the landlocked Great Lakes were historically protected. The seaway's canals and locks, completed in 1959 after decades of planning and five years of round-the-clock construction, bypass such drops as Niagara Falls and allow over 6,000 ships to sail in and out of the Great Lakes every year.

The initial impetus for canal construction came from the steel industries of Ohio and Pennsylvania. During the first half of this century, these industries relied on rich ore supplies from the Mesabi iron range in northern Minnesota. The end of this source was in sight by the 1930s; mining engineers pointed to remote but rich iron deposits in Labrador as the next alternative. Lacking a cheap transport method from Labrador to the Midwest, steel industry backers began lobbying for the St. Lawrence Seaway. Midwestern grain traders and manufacturers joined the effort, promoting the route as a public works and jobs project, an economic booster for inland states and provinces, and a symbol of joint United States and Canadian cooperation, power, nationalism, and progress.

Unfortunately the seaway and its heavy traffic have also brought modern problems to the Great Lakes. Aside from the petroleum and chemical leaks associated with active shipping routes, the seaway opened the Great Lakes to aggressive foreign animal and plant invaders. The world's largest freshwater ecosystem , the Great Lakes, had been isolated from external invasion by steep waterfalls and sheer distance until the canals and locks opened. Since the 1960s, an increasing number of Atlantic, European, and Asian species have spread through the lakes. Some arrive under their own power, but most appear to have entered with oceangoing ships. Until recently, ships arriving at Great Lakes ports commonly carried freshwater ballast picked up in Europe or Asia. When the ships reached their Great Lakes destinations they discharged their ballast and loaded grain, ore, automobiles, and other goods. A profusion of plankton and larvae riding in the ballast water thus entered a new environment ; some of them thrived and spread with alarming speed.

One of the first introduced species to make its mark was the lamprey (Petromyzon marinus ), an 18in (45.7 cm) long, eel-shaped Atlantic species that attaches itself to the side of a fish with its circular, suction-like mouth. Once attached, the lamprey uses its rasping teeth to feed on the fish's living tissue, usually killing its host. After the lamprey's arrival in the 1960s, Lake Superior's commercial whitefish and trout fisheries collapsed. Between 1970 and 1980, Great Lakes trout and salmon populations plummeted by 90%. The region's $2 billion per year sport fishery nearly disappeared with commercial fishing . Since the 1970s, innovative control methods such as carefully-timed chemical spraying on spawning grounds have reduced lamprey populations, and native game fish have shown some recovery.

However, many other invaders have reached the Great Lakes via the seaway. Tubenose gobies (Proterorhinus marmoratus ), a bottom-dwelling fish from the Black Sea, compete for food and spawning grounds with native perch and sculpins. The prolific North European ruffes (Gymnocephalus cernuus, a small perch) and spiny water flea (Bythotrephes cederstroemi, a tiny crustacean) also compete with native fish, and having hard, sharp spines, both are difficult for other species to eat. Asian invaders include the Asiatic clam (Corbicula fluminea ), which colonizes and blocks industrial water outlets.

Most threatening to the region's businesses and economies is the zebra mussel (Dreissena polymorpha ). Originating in the Baltic region, this tiny, extraordinarily prolific bivalve colonizes and suffocates industrial water pipes, docks, hard lake-bottom surfaces, and even the shells of native clams. Ironically, the zebra mussel has also benefited the lakes by raising public awareness of exotic invasions. Alarmed industries and states, faced with the enormous cost of cleaning and replacing zebra mussel-clogged pipes and screens, have begun supporting laws forcing incoming ships to dump their ballast at sea. Although reversals of exotic invasions are probably impossible, such remedial control measures may help limit damages.

See also Biofouling; Exotic species; Introduced species; Parasites; Water pollution

[Mary Ann Cunningham Ph.D. ]



Cunningham, W. Understanding Our Environment: An Introduction. Dubuque, IA: William C. Brown, 1994.

Mabec, C. The Seaway Story. New York: Macmillan Co., 1961.


Raloff, J. "From Tough Ruffe to Quagga: Intimidating Invaders Alter the Earth's Largest Freshwater Ecosystem." Science News 142 (July 25, 1992): 568.


St. Lawrence Seaway: 1991 Navigation Season. Ottawa: Saint Lawrence Seaway Authority.

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St. Lawrence Seaway