Mississippi River System

The Mississippi River System, also referred to as the Western Rivers and Mississippi-Missouri Basin, is a mostly riverine network of the United States which includes the Mississippi River and connecting waterways. The Mississippi River is the largest drainage basin in the United States. In the United States, the Mississippi drains about 41% of the country's land area.

From the perspective of natural geography and hydrology, the system consists of the Mississippi River itself and its numerous natural tributaries and distributaries. The major tributaries are the Arkansas, Illinois, Missouri, Ohio and Red rivers. Given their flow volumes, major Ohio River tributaries like the Allegheny, Tennessee, and Wabash rivers are considered important tributaries to the Mississippi system. Before the Mississippi River reaches the Gulf of Mexico, it runs into its distributary, the Atchafalaya River.

From the perspective of modern commercial navigation, the system includes the above as well as navigable inland waterways which are connected by artificial means. Important connecting waterways include the Illinois Waterway, the Tennessee-Tombigbee Waterway, and the Gulf Intracoastal Waterway. This system of waterways is maintained by the U.S. Army Corps of Engineers with a project depth of between 9–12 ft (2.7–3.7 m) to accommodate barge transportation, primarily of bulk commodities.

The Mississippi River carries 60% of U.S. grain shipments, 22% of oil and gas shipments, and 20% of coal.

The Upper Mississippi River spans around 1,250 miles (2,010 km) from Lake Itasca in Minnesota to Cairo, Illinois. Most of the Upper Mississippi goes through the center of the Driftless Area, around 15,000 sq mi (39,000 km²) in Minnesota, Wisconsin, Iowa, and Illinois that has managed to stay free of glacial flows covering the past two million years. The Driftless Area is defined by a multitude of limestone bluffs that have been molded all the way since the last ice age, due to water melting from glaciers. The bottom of the river is composed of a thin layer of clay, silt, loam, and sand, which lay above a stratum of glacial outwash.

The Upper Mississippi River covers approximately half of the Mississippi River's length. About 850 miles (1,370 km) of the river is navigable from Minneapolis-St. Paul (specifically, the Coon Rapids Dam in the City of Coon Rapids, MN) to the Ohio River. The river sustains a large variety of aquatic life, including 127 species of fish and 30 species of freshwater mussels.

The Arkansas River is one of the major tributaries in the Mississippi River system. It flows west to east starting in Colorado and dumping into the Mississippi River. Its length of 1,469 miles (2,364 km) allows it to flow through Colorado, Kansas, Oklahoma, and Arkansas. It is the sixth-longest river in the US, the second-longest tributary to the Mississippi River System, and the 45th longest river in the world.

The Illinois River is a principal tributary of the Mississippi River. The river runs approximately 273 miles (439 km) long, in the U.S. state of Illinois. This river was important among Native Americans and early French traders as the principal water route connecting the Great Lakes with the Mississippi. The Illinois River meets the Mississippi at Pere Marquette State Park, which is near Grafton.