Missouri River

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Missouri, river, c.2,565 mi (4,130 km) long (including its Jefferson-Beaverhead-Red Rock headstream), the longest river of the United States and the principal tributary of the Mississippi River. The length of the combined Missouri-Mississippi system from the headwaters of the Missouri to the mouth of the Mississippi is c.3,740 mi (6,020 km), making it the world's third longest river after the Nile and the Amazon. The Missouri River drains an area of c.580,000 sq mi (1,502,200 sq km), including 2,550 sq mi (6,600 sq km) in Canada.


The principal headwaters of the Missouri are the Jefferson, Madison, and Gallatin rivers, which rise high in the Rocky Mts., SW Mont., and join to form the Missouri near Three Forks, Mont. The Missouri's upper course flows north through scenic mountain terrain including Gate of the Mountains, a deep gorge. At Great Falls, Mont., the river enters a 10-mi (16-km) stretch of cataracts that prevented navigation to the upper river and effectively established Fort Benton, Mont., as the head of navigation for 19th-century riverboats. Below Fort Benton the Missouri follows a meandering course east through the unspoiled Missouri Breaks and Fort Peck Lake (behind Fort Peck Dam) then southeast through the dammed Lakes Sakakawea and Oahe and across the Great Plains of the W central United States, crossing Montana, North Dakota, and South Dakota, and forming part of the boundaries of Nebraska, Kansas, and Iowa before crossing Missouri and entering the Mississippi River 17 mi (27 km) N of St. Louis. Nicknamed "Big Muddy" for its heavy load of silt, the brown waters of the Missouri do not readily mix with the gray waters of the Mississippi until c.100 mi (160 km) downstream. The Yellowstone and Platte rivers are the Missouri's chief tributaries.

Human Impact and Use

Above Sioux City, Iowa, the Missouri's fluctuating flow is regulated by seven major dams (Gavins Point, Fort Randall, Big Bend, Oahe, Garrison, Fort Peck, and Canyon Ferry) and more than 80 other dams on tributary streams. These dams, with their reservoirs, are part of the coordinated, basin-wide Missouri River basin project (authorized by the U.S. Congress in 1944), which provides for flood control, hydroelectric power, irrigation water, and recreational facilities. The dams serve to impound for later use the spring rains and snowmelt that swell the volume of the river in March and April and also the second flood stage that frequently occurs in June as the snow melts in the remoter mountain regions. Despite this system of dams, during the extremely rainy summer of 1993 the lower Missouri reached record levels, flooding many areas, eroding farmland, and depositing huge quantities of sand that damaged many thousands of acres of fertile bottomland. Flooding was also a significant problem along the river in 2011.

Since the dams have no locks, Sioux City is the head of navigation for the 9-ft (2.7-m) channel maintained over the 760-mi (1,223-km) stretch downstream to the Mississippi. Tugboats pushing strings of barges move freight along this route. From December to March, navigation is interrupted by ice and low water levels (resulting from upstream freezing); summer water levels, which frequently fell so low as to cause river boats to go aground, are now maintained at safe levels by the release of water from Gavin Point Dam. Silt, fertilizers, and pesticides, which are contained in the runoff from agricultural lands, pollute the water above Sioux City, but wastes from industrial plants and from inadequately treated municipal sewage create a more serious level of pollution downstream. There has been a reduction in wetland areas and a loss of fish and wildlife due to the damming of the river.


The Missouri River was an important artery of commerce for Native American villages of the Plains culture long before Europeans arrived. The French explorers Jacques Marquette and Louis Jolliet passed the mouth of the river in 1683 and the Canadian explorer Vérendrye visited the upper reaches of the river in 1738. David Thompson, a Canadian fur trader, explored part of the river in 1797. Meriwether Lewis and William Clark followed the Missouri on their journey (1803–6) to the Pacific Ocean and described it at length (see Lewis and Clark expedition). The first steamboat ascended the river in 1819, and hundreds more later navigated the uncertain waters to Fort Benton. Mormons bound for Utah and pioneers bound for Oregon and California followed the Missouri valley and that of the Platte overland to the West. River traffic declined with the loss of freight to the railroads after the Civil War. Although it was revitalized in the mid-20th cent., in the section below Sioux City, through the navigational improvements and flood control efforts of the Missouri River basin project, barge traffic declined in the late 20th cent. Two stretches of the river are protected as the Missouri National Recreational River (see National Parks and Monuments (table)).


See B. De Voto, Across the Wide Missouri (1947, repr. 1972); H. M. Chittenden, Early Steamboat Navigation on the Missouri River (1972); B. Priddy, Across Our Wide Missouri (2 vol., 1982–84).

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MISSOURI RIVER, in the central and northwest central United States, is a major tributary of the Mississippi River and the longest river in the United States (2,466 miles). It drains a watershed of approximately 580,000 square miles. Father Jacques Marquette and Louis Jolliet reached the mouth of the Missouri in 1673. It was known to them as Peki-tan-oui, so named on some of the early maps, and later as Oumessourit. From its source in southwestern Montana, where the Jefferson, Gallatin, and Madison Rivers join together, it winds around hills and bluffs, through one of the most fertile valleys in the world, to its junction with the Mississippi (ten miles north of Saint Louis).

The lower part of the Missouri was known to the French trappers, traders, and voyageurs, who ascended it as far as the Kansas River in 1705. In 1720 a Spanish caravan was sent from Santa Fe to the Missouri to drive back the French. The early French called the river Saint Philip. They probably did not go higher than the Platte, which was considered the dividing line between the upper and lower river. In 1719 Claude Charles du Tisne and party went up the Missouri in canoes as far as the Grand River. Credited with being the first white man to visit the upper Missouri country, Pierre Gaultier de Varennes, Sieur de La Vérendrye, led a party from one of the posts of the Hudson's Bay Company in 1738 to the Mandan villages. Other explorations followed, searching for the "Western Sea" by way of the Missouri River. The Missouri was first explored from its mouth to its source by Meriwether Lewis and William Clark (1804–1805).

Although it was thought for years that no keelboat could ascend the Missouri, it later became the great highway into the West. Gregoire Sarpy is said to have first introduced the keelboat, but the real father of navigation on the Missouri was Manuel Lisa. The first steamboat ever to ascend the river was the Independence, which pushed off from Saint Louis in 1819, reached Old Franklin in thirteen days, and turned back at Old Chariton, in Missouri. In 1831, Pierre Chouteau succeeded in ascending the Missouri in his steamboat Yellowstone. As a result of steamboating, many cities grew up along the edge of the river and several states built their capitals on its bank. Steamboating on the river reached its peak in the late 1850s and declined following the completion in 1859 of the Hannibal and Saint Joseph Railroad.

The Missouri River has always carried in suspension an immense amount of solid matter, mostly very fine light sand, discoloring the water and justifying the name of "Big Muddy." It is said that the yearly average of solid matter carried into the Mississippi by this river is over 500 million tons, brought along for an average distance of 500 miles. While the Missouri has a greater annual flow of water than the Mississippi above its mouth, it is subject to greater fluctuations. These have affected its navigability in certain seasons and caused the shoreline to shift, some farms and villages to disappear, and others to be left far back through deposits of the soil in front of them.

In 1944 Congress authorized a Missouri River basin project to control flooding of the Missouri, improve navigation, develop hydroelectric power, irrigate more than 4.3 million acres in the basin, halt stream pollution, and provide recreation areas. By the 1970s there were seven dams on the Missouri and eighty on its tributaries. The Missouri Basin Interagency Committee, with representatives from seven federal agencies and the governors of the ten Missouri basin states (North Dakota, South Dakota, Wyoming, Nebraska, Kansas, Minnesota, Missouri, Colorado, Iowa, and Montana), oversees the project. In the late twentieth century, the urbanization, soil erosion, and pollution had made the Missouri River one of the nation's most endangered rivers.


Brower, Jacob V. The Missouri River and Its Utmost Source; Curtailed Narration of Geologic, Primitive and Geographic Distinctions Descriptive of the Evolution and Discovery of the River and Its Headwaters. St. Paul, Minn.: Pioneer Press, 1896, 1897.

DeVoto, Bernard A. Across the Wide Missouri: 1897–1955. Boston: Houghton Mifflin, 1947, 1987; New York: American Legacy Press, 1981.

Griffith, Cecil R. The Missouri River: The River Rat's Guide to Missouri River History and Folklore. Leawood, Kans.: Squire Publishers, 1974.

Stella M.Drumm/a. g.

See alsoKansas City ; Lewis and Clark Expedition .

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The Missouri River is the longest river in the United States. It flows for 2,466 miles (3,968 kilometers). Its source lies in the Rocky Mountains of southwestern Montana; the river is formed by the confluence of the Jefferson, Madison, and Gallatin rivers at Three Forks, Montana. From there the Missouri flows east and southeast, ultimately joining the Mississippi River about 10 miles (16 kilometers) north of St. Louis, Missouri. The Missouri River flows through Montana, North Dakota, South Dakota, Nebraska, Iowa, Kansas, and Missouri. From the Mississippi River, the Missouri is navigable by barges and towboats west and north as far as Sioux City, Iowa. Above Sioux City the water flow is controlled by a series of dams in a project authorized by the U.S. government in 1944. When the water is high the river is navigable to Great Falls (northeast of Helena), Montana.

In 1673 the mouth of the Missouri was passed by French-Canadian adventurer Louis Jolliet (16451700) and French missionary Jacques Marquette (163775) as they explored the upper part of the Mississippi River. The Lewis and Clark expedition of 180406 followed the Missouri for much of the journey to the Pacific Ocean.

During the first two decades of the 1800s, the river provided a chief transportation route for the western fur trade, which relied on keel boats to move goods along the river. In 1819 steamboat traffic began on the waterway, carrying pioneers to the rugged West. Riverboat traffic declined with the expansion of the cross-continental railroads at the end of the nineteenth century. Much of the region through which the Missouri River flowsthe interior plainswas the last frontier to be settled in America.

See also: Fur Trade, Louisiana Purchase, Lewis and Clark Expedition, Mississippi River, Steamboats

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Missouri (‘Big Muddy’) Longest river of the USA; the major tributary of the Mississippi. It rises at the confluence of the Jefferson, Madison and Gallatin rivers in the Rocky Mountains, Montana. It then flows e through Great Falls cataracts and Fort Peck reservoir. In North Dakota it turns se across the Great Plains, passing through Omaha and Kansas City. It joins the Mississippi River, 27km (17mi) n of St Louis. Sioux City, Iowa, is the head of navigation. Seasonal fluctuation in flow is a major problem, and the Missouri has seven major dams. Its major tributaries are the Yellowstone and Platte rivers. Native Americans used the river as a trade route for centuries before its discovery (1683) by the explorers Marquette and Jolliet. Mapped by the Lewis and Clark Expedition (1804–06), traders, gold seekers, and pioneers used the river as a route to the nw. Length: c.4120km (2560mi).