The Mississippi River

Matthews, Missouri

October 14, 2022

The Mississippi River is 2,348 miles long, the second-longest river in the United States after the Missouri River. Its source begins at Lake Itasca, 1,475 feet above sea level in Itasca State Park, Minnesota. The river falls to 725 feet just below Saint Anthony Falls in Minneapolis; the only waterfall along the river's course. The Mississippi passes through several glacial lakes, pine forests, vegetation and cattail marshes before it is joined by tributaries. The retention time from its beginning at Lake Itasca to the end at the Gulf of Mexico is about 90 days.

The Minnesota River and the Illinois River are among the first to join the Mississippi. The Missouri River joins the Mississippi near St. Louis, Missouri. Sometimes referred to as "The Big Muddy," it is the Mississippi's second largest tributary by volume. The Mississippi is also joined by the Ohio River at Cairo, Illinois and the Arkansas River near Arkansas Post, Arkansas. The Atchafalaya River in Louisiana is a major distributary of the Mississippi.

Its triangular drainage area covers about 40 percent of the U.S. and includes all or part of 31 states. It drains most of the area between the Rocky Mountains and the Appalachian Mountains except for the areas drained by Hudson Bay via the Red River of the north, the Great Lakes and the Rio Grande.

The Mississippi forms the borders of eight states: Wisconsin, Iowa, Illinois, Missouri, Kentucky, Arkansas, Tennessee and Mississippi. It runs through two others: Minnesota and Louisiana. The river empties into the Gulf of Mexico about 100 miles downstream from New Orleans, Louisiana.

From its source to the Ohio River, the river is called the Upper Mississippi River, from the Ohio to its mouth it is known as the Lower Mississippi. The Upper Mississippi is further divided into three sections:

• the headwaters, from the source to Saint Anthony Falls

• a series of man-made lakes between Minneapolis and St. Louis, Missouri

• the middle Mississippi, a relatively free-flowing river downstream of the confluence with the Missouri River at St. Louis

A series of 29 locks and dams on the upper Mississippi, most of which were built in the 1930s, is designed primarily to maintain a nine-foot deep channel for commercial barge traffic.

The lakes formed are also used for recreational boating and fishing. The dams make the river deeper and wider, but do not stop it. During periods of high flow, the gates, some of which are submersible, are completely opened and the dams simply cease to function. Below St. Louis, the Mississippi is relatively free-flowing, although it is constrained by numerous levees and directed by numerous wing dams.

Through a natural process known as deltaic switching, the lower Mississippi River has shifted its final course to the ocean every thousand years or so. This occurs because the deposits of silt and sediment raise the river's level causing it to eventually find a steeper route to the Gulf of Mexico. The abandoned distributary diminishes in volume and forms what are known as bayous. This process has, over the past five thousand years, caused the coastline of south Louisiana to advance toward the Gulf from 15 to 50 miles (25–80 kilometers).

The Mississippi River Delta Basin is defined as all of the land and shallow estuarine area between the two northernmost passes of the Mississippi River and the Gulf of Mexico. The basin is located in Plaquemines Parish, Louisiana, south of the city of Venice.