Basin and Tributaries

Water from 31 states and 2 Canadian provinces drains into the Mississippi. Its basin, shaped roughly like a triangle, stretches from the Appalachians to the Rocky Mountains and tapers southward to the delta. The basin's area is about 1,244,000 square miles (3,222,000 km 2), or about 40 per cent of the area of the 48 contiguous states.

Thousands of rivers and streams flow into the Mississippi to form its drainage system. The Missouri River is by far the longest tributary—only 33 miles (53 km) shorter than the Mississippi itself. The Mississippi-Missouri-Red Rock, with a length of 3,741 miles (6,021 km), ranks among the world's largest river systems. The Ohio River, at its mouth near Cairo, Illinois, delivers a flow as large as the combined Missouri-Mississippi.

Other tributaries in the north include the Minnesota and St. Croix rivers in Minnesota, the Chippewa and Wisconsin rivers in Wisconsin, the Rock and Illinois rivers in Illinois, and the Iowa and Des Moines rivers in Iowa. Major tributaries in the south include the White and Arkansas rivers in Arkansas and the Yazoo River in Mississippi.