The Missouri River: America's Longest River

The Missouri River—2,341 miles (3,768 km) from Brower's Spring, Montana to its Mississippi confluence at St. Louis—edges out the Mississippi (2,320 miles from Lake Itasca) as the United States' longest river. Together, they form the world's 4th longest river system (3,902 miles / 6,275 km).

Source to Mouth Journey

Montana: Mountain Birth

• Ultimate source – Brower's Spring (8,800 ft), Centennial Mountains; Hell Roaring Creek → Red Rock River
• Official source – Madison/Jefferson/Gallatin confluence at Three Forks (4,045 ft)
• Great Falls – Five waterfalls (Lewis & Clark portage); now 5 dams
• Fort Peck Dam – 1940; 134-mi reservoir; 185 MW

North Dakota: Reservoir State

• Lake Sakakawea – Garrison Dam (1953); 178 mi; 382 MW; 3rd largest US reservoir
• Free-flowing reach – 60 mi Bismarck to Oahe headwaters; cottonwood galleries

South Dakota: Lake Chain

• Lake Oahe – Oahe Dam (1962); 231 mi; 786 MW; 4th largest reservoir
• Lake Sharpe – Big Bend Dam (1963); 80 mi
• Lake Francis Case – Fort Randall Dam (1956); 107 mi
• Lewis & Clark Lake – Gavins Point Dam (1957); 25 mi; last dam

Nebraska: Border River

• Channelized – 735 mi engineered channel (Sioux City to St. Louis)
• Omaha/Council Bluffs – Major metro crossing; Bob Kerrey Pedestrian Bridge
• Platte River confluence – Major tributary; sandhill crane migration

Missouri: Final Stretch

• Kansas City – Bend point; west-east turn
• Missouri River Valley – Wide floodplain; agriculture, wetlands
• Confluence – Mississippi River at St. Louis (Gateway Arch frames view)

Hydrology and Management

• Drainage basin – 529,350 mi² (1/6 of US); 10 states + 2 Canadian provinces
• Average discharge – 86,000 cfs (2,435 m³/s) at Hermann, MO
• Sediment load – Historically 100-400M tons/yr ("Big Muddy"); now ~20M (trapped by dams)
• Pick-Sloan Plan – 1944 Flood Control Act; 6 mainstem dams + tributary projects
• Master Manual – 8 competing purposes; annual operating plan; litigation constant

Ecological and Cultural Significance

• Pallid sturgeon – Endemic, endangered; 70M-year lineage; dam-blocked reproduction
• Least tern / Piping plover – Nest on sandbars; flow management for habitat
• Lewis & Clark Trail – 4,900 miles; follows Missouri 2,500+ miles
• Native nations – 28 tribes; Mandan, Hidatsa, Arikara (Three Affiliated), Lakota, Crow, Omaha
• Steamboat era – 1819-1880s; "Mountain boats" to Fort Benton (3,000 mi navigable)

Climate Vulnerability

Snowpack decline (Rockies -20% since 1950), earlier runoff, increased evaporation, and extreme events (2011 flood, 2012 drought) challenge the engineered system. Missouri River Recovery Program attempts ecosystem restoration within authorization constraints.