North America's Second-Longest River: The Mighty Missouri

While the Mississippi River claims the title of North America's longest river (2,340 miles from Lake Itasca to the Gulf), its greatest tributary—the Missouri River—holds second place at approximately 2,341 miles from its Montana headwaters to its confluence with the Mississippi near St. Louis.

Ironically, the Missouri is longer than the Mississippi above their junction. If measured from the Missouri's ultimate source (Brower's Spring, Montana) to the Gulf, the combined Mississippi-Missouri system stretches ~3,710 miles—making it the world's fourth-longest river system after the Nile, Amazon, and Yangtze.

The Missouri drains a vast watershed across ten U.S. states and two Canadian provinces, shaping the Great Plains' ecology, history, and economy—from Lewis and Clark's expedition to modern agriculture and hydroelectric power.