Missouri River

The Missouri River is a major river of central North America, and is a tributary of the Mississippi River. It is the longest river by name on the continent at 2,341 miles (3,767 km), and the second largest tributary of the Mississippi by discharge, after the Ohio. The watershed of the Missouri River drains nearly 530,000 square miles (1,400,000 km²) of the Great Plains east of the Rocky Mountains, spanning parts of ten U.S. states and two Canadian provinces. Around 10 million people live in the basin, many concentrated in urban centers along the main stem such as St. Louis; Kansas City; Omaha; Sioux City; and Great Falls. Measured from its hydrologic source in the Centennial Mountains of Montana to the Mississippi's mouth at the Gulf of Mexico, it forms part of the fourth-longest river system in the world.

As early as 12,000 years ago, Paleo-Indians settled in the plains of the Missouri River basin. Prominent Native American tribes that lived on the river in immediate pre-Columbian times included the Mandan, Sioux, Hidatsa, Osage, and Missouria – the latter for whom the river is named. European and American explorers wandered the region in the 1700s and 1800s, when the Missouri basin became part of France's Louisiana territory. When Louisiana was sold to the United States, the Lewis and Clark Expedition traveled the river in search of a route to the Pacific coast of North America. Settlers' expansion into the Great Plains pushed Native Americans out of their traditional lands, leading to wars. The Missouri River served as a boundary for the American frontier in the 19th century, and many prominent westward routes such as the Oregon Trail had their starting points on the river.

Although it once was by far the longest river of North America, today its length is comparable with the Mississippi because of channelization to eliminate meanders and facilitate navigation. The lower Missouri valley has become a highly productive agricultural and industrial region. Barges shipping gravel, wheat, fertilizer, and other grown, mined or manufactured products provide most river commerce today. In response to the growing amount of water traffic, federal and state agencies including the U.S. Army Corps of Engineers (USACE) heavily dammed and channelized the river in the 20th century. Although this development has contributed to the region's economic growth, it has taken a toll on the ecology and the water quality of the Missouri.

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