Missouri River (United States)

Missouri River (United States)
Christopher Michel · CC BY-SA 4.0 · source
Name	Missouri River
Country	United States
State	Montana, North Dakota, South Dakota, Nebraska, Iowa, Kansas, Missouri
Length km	3767
Source	Confluence of Madison River, Gallatin River, Jefferson River
Source location	near Three Forks, Montana
Mouth	Confluence with the Mississippi River
Mouth location	near St. Louis
Basin countries	United States

Contents

Missouri River (United States) The Missouri River is the longest river in the United States, rising in the Rocky Mountains and flowing east and south to join the Mississippi River near St. Louis. It traverses headwaters and plains across Montana, North Dakota, South Dakota, Nebraska, Iowa, Kansas, and Missouri, shaping settlement, transport, and ecosystems from the era of Lewis and Clark Expedition through modern infrastructure projects like the Pick–Sloan Missouri Basin Program and the Fort Peck Dam system.

Course and Geography

The Missouri River originates at the confluence of the Jefferson River, Madison River, and Gallatin River near Three Forks, Montana and flows past Helena, Montana, Fort Peck, Montana, and Bismarck, North Dakota before turning southeast past Pierre, South Dakota, Sioux City, Iowa, and Omaha, Nebraska, continuing along the border of Kansas and Missouri and merging with the Mississippi River near St. Louis, Missouri. Along its course it crosses diverse physiographic provinces including the Cordilleran Ice Sheet-influenced valleys, the Great Plains, and the Missouri Alluvial Plain, interacting with features such as the Badlands National Park region, the Upper Missouri River Breaks National Monument, and the Missouri Breaks. The corridor includes major floodplains, oxbow lakes, and channel systems shaped by historic events like the Great Flood of 1993 and engineering works including the Garrison Dam and Fort Peck Lake reservoirs.

The Missouri River drainage basin receives runoff from tributaries including the Yellowstone River, Platte River, Kansas River, Big Sioux River, James River (Dakotas), and Milk River, among others; headwater streams include the Musselshell River and the Big Horn River. Flow regimes are influenced by snowmelt in the Rocky Mountains, precipitation events tied to El Niño–Southern Oscillation phases, and reservoir regulation by entities such as the U.S. Army Corps of Engineers and the Bureau of Reclamation. Hydrological measurements at gaging stations near Omaha, Nebraska, St. Louis, Missouri, and Bismarck, North Dakota document seasonal discharge variability, sediment transport from the Powder River and Little Missouri River, and historical navigability issues addressed in treaties like the Louisiana Purchase aftermath. Flood control and sediment management link to programs enacted after catastrophes like the Great Flood of 1881 and later coordinated under the Pick–Sloan Missouri Basin Program.

Indigenous nations including the Sioux, Cheyenne, Omaha, Otoe–Missouria Tribe, Assiniboine, and Mandan occupied and used the Missouri River corridor for centuries prior to European contact. Early European exploration featured Jacques Marquette-era impulses and later expeditions culminating in the Lewis and Clark Expedition, which established winter quarters at Fort Mandan and mapped the river during the Corps of Discovery journey. The river became a conduit for the Fur trade involving enterprises like the American Fur Company and figures such as Meriwether Lewis, William Clark, York, Sakakawea, and Toussaint Charbonneau. Military and settlement history includes Fort Benton (Montana), the Oregon Trail and Santa Fe Trail intersections, conflicts such as the Battle of the Little Bighorn context, and later development under policies influenced by the Homestead Act and federal water law precedents adjudicated by the Supreme Court of the United States.

The Missouri River corridor hosts infrastructure like the Fort Peck Dam, Garrison Dam, Oahe Dam, Big Bend Dam, Fort Randall Dam, and Gavins Point Dam, built under programs such as the Pick–Sloan Missouri Basin Program to provide flood control, hydroelectric power, irrigation, and navigation improvements. Navigation projects included channelization, levees, and the 9-foot navigation channel promoted by the U.S. Army Corps of Engineers in coordination with the Missouri River Basin Association and transport interests such as Bunge Limited-operated river terminals and Cargill facilities. Urban infrastructure along the river serves cities like St. Louis, Kansas City, Missouri, Omaha, Nebraska, Sioux City, Iowa, and Bismarck, North Dakota with ports, bridges (including the Eads Bridge and Hermann Bridge), and water treatment works tied to agencies like the Environmental Protection Agency and regional compacts including the Interstate Commission on the Missouri River Basin.

The Missouri River supports habitats for species such as the Pallid sturgeon, Scaphirhynchus albus, Piping plover, Least tern, white sturgeon, Northern pike, and migratory waterfowl using the Mississippi Flyway linkage. Riparian zones contain plant communities including cottonwood stands and wetlands managed by agencies such as the U.S. Fish and Wildlife Service and conservation organizations like the Audubon Society and The Nature Conservancy. Environmental challenges include habitat fragmentation from dams, altered sediment regimes affecting river morphology, invasive species like Zebra mussel and Common carp, and water quality issues addressed under statutes like the Clean Water Act. Restoration and mitigation programs involve partnerships with the Bureau of Land Management, tribal governments such as the Oglala Sioux Tribe, and research conducted by institutions like the University of Missouri and Montana State University.

The river underpins commercial activities including barge transport of grain and coal linked to agribusiness firms such as Archer Daniels Midland, Cargill, and Mosaic Company, as well as recreational economies centered on angling, boating, hunting, and tourism around sites like Lewis and Clark National Historic Trail, Lake Sakakawea, Gavins Point National Fish Hatchery, and state parks in Nebraska, South Dakota, and Missouri. Recreational outfitters, marinas, and events in cities like Kansas City and St. Louis collaborate with agencies such as the National Park Service and U.S. Forest Service to manage access, safety, and cultural interpretation. Economic debates continue over navigation investments advocated by stakeholders including the American Waterways Operators and conservation priorities championed by groups such as the Sierra Club and National Wildlife Federation.