The Mississippi River The Mississippi River, 3,779 km (2,348 mi) long, is the second longest river, after the Missouri, in the United States. Its triangular drainage area, covering about 40% of the country and including all or part of 31 states, is approximately 3,250,000 sq km (1,250,000 sq mi), the third largest in the world. The Mississippi rises in Minnesota and then flows south, following the boundaries between the states of Minnesota, Iowa, Missouri, Arkansas, and Louisiana on the west, and Wisconsin, Illinois, Kentucky, Tennessee, and Mississippi on the east. The river, whose name means “father of waters” in the Algonquian language, has long been an important transportation artery of North America. Course of the River Rising at an elevation of 446 m (1,463 ft) in Lake Itasca, Minn., the Mississippi flows through several glacial lakes to Minneapolis-Saint Paul, where it passes over a series of rapids and is joined by the Minnesota River. After this confluence, the Mississippi is fringed by 60-90-m-high (200-300-ft) bluffs on both sides. Between Minneapolis and Saint Louis, Mo., the most important tributaries are the Illinois, Chippewa, Black, Wisconsin, Saint Croix, Iowa, Des Moines, and Rock rivers, some of which drain the nation’s most fertile agricultural areas. The Missouri river, draining the Great Plains to the west, joins the Mississippi at Saint Louis. It is the longest tributary, and constitutes more than 40% of the Mississippi system drainage area, while furnishing about 20% of the total discharge. At Cairo, Ill., the Mississippi is joined from the east by the Ohio river.
South of Cairo the Mississippi enters a wide (64-113 km/40-70 mi), low valley that was once an embayment of the Gulf of Mexico. Sediment has filled this area, and through the centuries the river has extended its mouth to the present location 966 km (600 mi) downstream. This lower part of the Mississippi’s course, characterized by geographers as a typical example of an “old-age” river, is contained within natural levees formed by flood-deposited sediments. Beyond the levees lie low floodplains often at a lower elevation than the river itself. Another feature of the river is its meandering. The channel route from Cairo to New Orleans is almost three times as long as the valley. Major tributaries in the lower section are the Arkansas, Red, and White rivers, all flowing from the west. The Mississippi enters the Gulf of Mexico about 160 km (100 mi) downstream from New Orleans, through a 26,150-sq km (10,100-sq mi) delta. Because almost 550 million metric tons (500 million U.S. tons) of sediment are deposited annually, the delta extends about 91 m (300 ft) each year.