Course of the Missouri River

The Missouri River rises in the Rocky Mountains of southwestern Montana at the confluence of the Jefferson River and Madison River, in Missouri Headwaters State Park near the town of Three Forks. It flows north, passing through Canyon Ferry Lake, west of the Big Belt Mountains. It exits from the mountains near Cascade, and flows northeast to the city of Great Falls, where it drops over the Great Falls of the Missouri, a series of five substantial cataracts. The Missouri then flows east through canyons and badlands, past the confluence with the Marias River, widening into the Fort Peck Lake reservoir near the confluence of the Musselshell River. Farther on the river passes through the gates of the Fort Peck Dam, and immediately after that, the Milk River enters from the left.

It flows eastwards through the plains of eastern Montana, receiving the Poplar River at Poplar before crossing into North Dakota where the Yellowstone River, its greatest tributary, joins from the right. At the confluence, the two rivers are approximately the same size. The Missouri then meanders east past Williston and into Lake Sakakawea, a reservoir formed by the Garrison Dam, where the river turns south. South of Riverdale, the Knife River enters from the right. The Missouri continues south to the city of Bismarck, the North Dakota state capital, where it receives the Heart River. It slows into the Lake Oahe reservoir just before the Cannonball River confluence. While it continues south, eventually reaching Oahe Dam in South Dakota, the Grand, Moreau and Cheyenne Rivers all join the Missouri from the right.

The Missouri makes a bend to the southeast as it meanders through the Great Plains, receiving the Niobrara River from the right. The Missouri then proceeds to form the boundary of South Dakota and Nebraska, then after it receives the James River, forms the Iowa-Nebraska boundary. At Sioux City the Big Sioux River comes in from the left. The Missouri flows south to the big city of Omaha where it receives one of its largest tributaries, the Platte River. Downstream of there, it begins to define the Nebraska-Missouri border, then flows between Missouri and Kansas. It turns east at Kansas City, where the Kansas River enters from the right, and so on into north-central Missouri. The river passes south of Columbia and receives the Osage River, its last major tributary, downstream of Jefferson City. It then rounds the northern side of St. Louis to join the Mississippi River on the border between Missouri and Illinois.

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