The Mississippi River has the third largest drainage basin in the world, exceeded in size only by the watersheds of the Amazon and Congo Rivers. It drains 41 percent of the 48 contiguous states of the United States. The basin covers more than 1,245,000 square miles, includes all or parts of 31 states and two Canadian provinces, and roughly resembles a funnel which has its spout at the Gulf of Mexico. Waters from as far east as New York and as far west as Montana contribute to flows in the lower river.
The Lower Mississippi River and its alluvial valley extend approximately 1,000 river miles from Cape Girardeau, Missouri, in the north to the Gulf of Mexico in the south. The lower alluvial valley encompasses about 35,000 square miles bordering on the river which would be overflowed during times of high water if it were not for man-made protective works. The lower valley varies in width from 25 to 125 miles and includes parts of seven states–Missouri, Illinois, Tennessee, Kentucky, Arkansas, Mississippi and Louisiana.
The Lower Mississippi River is the most heavily traveled segment of the river, with more than 20 percent of the U.S. waterborne commerce passing through it. The Port of South Louisiana, which stretches 54 miles along the Mississippi River is the largest tonnage port in the U.S. It is comprised of facilities in three parishes between New Orleans and Baton Rouge. In fiscal year 2010, it shipped 114 million short tons of cargo. Other top ports along the Lower Mississippi River include the Port of New Orleans (ranked 7th), the Port of Plaquemines, La. (11th) and the Port of Baton Rouge (13th).
In Louisiana, millions of dollars of business and thousands of jobs are related to the handling, financing, processing and transporting of cargo passing through the Lower Mississippi River. Much of the Midwest grain and crop production is exported from the U.S. via the Mississippi River, while crude oil represents the largest import commodity.
The Louisiana coast, through which the Mississippi River and its distributaries wind through, is also economically important to the nation. The Louisiana coast is home to 25 percent of commercial fisheries in the continental U.S., with more than one billion pounds caught annually. The fisheries have a dockside value of $291 million and a recreation value of $944 million. The catch is comparable to the entire Atlantic seaboard and is triple that of the remaining states along the Gulf of Mexico.
The Mississippi River is a migratory flyway for 60 percent of all North American birds (326 species) and 40 percent of migratory waterfowl. The river and its floodplain are also home to 260 species of fish (a quarter of all found in North America), 50 species of mammals, as many as 60 types of mussels and at least 145 species of amphibians and reptiles.
Much of the Lower Mississippi River is bound by levees, floodwalls and control structures as part of the Mississippi River & Tributaries (MR&T) project, a comprehensive, multi-state flood damage risk management program for the lower alluvial valley.
In addition to levees, the MR&T includes floodways to redirect excess flows away from the Mississippi River in times of high water. Three of the most notable floodways include the Birds-Point New Madrid Floodway in Missouri, the Morganza Floodway in south-central Louisiana and the Bonnet Carré Spillway in southeast Louisiana. The U.S. Army Corps of Engineers operated these three floodways simultaneously for the first time ever during the Flood of 2011, the largest recorded flood in the river’s history. Other components of the MR&T include channel improvement and stabilization for efficient navigation and risk reduction of the levee system, as well as reservoirs and pumping plants for flood drainage.