Missouri River

Major North American river rising in the Rocky Mountains; the Missouri is the continent's longest river and a principal tributary of the Mississippi, important for navigation, water supply, and history.

Overview

The Missouri River is a principal waterway of the central United States. It rises in the Rocky Mountains of western Montana and flows generally east and south before joining the Mississippi River near St. Louis. Often called the "Big Muddy," it carries large sediment loads and drains a vast region of plains, prairies and foothills. For many purposes the Missouri is considered the longest river in North America, and it serves as a major natural corridor for commerce, agriculture and wildlife.

Course and characteristics

The Missouri begins where several mountain streams converge in western Montana and travels through states including Montana, North Dakota, South Dakota, Nebraska, Iowa, Kansas and Missouri. Its watershed encompasses varied landscapes and climates. Along its course the river has been modified by a series of dams and reservoirs that regulate flow, reduce flooding and provide water storage. See regional maps and data via river maps and state resources at regional planning sites.

Human history and exploration

The river has long been central to Indigenous peoples and later European-American exploration. It became famous in the early 19th century as the route followed by the Lewis and Clark expedition. Through the 19th and 20th centuries the Missouri supported steamboat commerce, settlement of the Great Plains and projects to control floods and provide irrigation. Historical accounts and expedition records can be found through archives and educational portals such as historical collections.

Uses, management and ecology

Today the Missouri River system is managed for multiple uses: navigation, hydroelectric power, flood control, irrigation and municipal water supply. Management involves trade-offs between human needs and ecological functions; channelization and reservoirs have altered habitats for fish and birds. Conservation programs and research institutions work to restore riparian zones and balance competing uses. For technical and policy materials, consult government and academic resources like policy summaries.

Notable facts and distinctions

The Missouri is a major tributary of the Mississippi and, by many measures, the longest river in North America.
Its basin supports agriculture across large swaths of the Great Plains and provides key water storage behind large reservoirs.
Ongoing restoration and management efforts address sediment, flood risk and native species conservation; see research portals at scientific resources.

The Missouri remains both a working river—shaped by dams, navigation channels and levees—and a landscape with continuing cultural, ecological and economic importance. It is studied and monitored by federal, state and local agencies as well as universities and community groups working to understand and steward this complex river system.