Mississippi River

• Category: Inland Aquatic Biomes
• Geographic Location: North America
• Summary: An expansive area that drains more than 41 percent of the continental United States, the natural landscape of the Mississippi River basin varies widely, including floodplains, wetlands, forests, and glacial lakes that support vast numbers of aquatic, avian, and terrestrial species.

The Mississippi River is the largest river system in North America and the longest when combined with its largest tributary, the Missouri River. Globally, the Mississippi is the fourth-longest river when the length of the Missouri-Jefferson (Red Rock) system is included; however, the Mississippi River proper is the twentieth-longest river in the world. It begins in Minnesota and flows south for 2,340 miles (3,765 kilometers) to drain into the Gulf of Mexico near New Orleans, Louisiana. The river basin covers more than 41 percent of the continental United States, stretching across thirty-one states. It has played a crucial role in shaping the culture, economy, and environment of the United States since long before its founding.

Tribal groups such as the Choctaw, Ojibwa, Koroa, Chickasaw, Tunica, Yazoo, Pascagoula, Natchez, and Alibamu inhabited the basin centuries before the arrival of Europeans. During the period of colonial rule, France and Spain controlled much of the river basin before the country’s Louisiana Purchase in 1803. The expansion of settlements along the river increased with the advent of the paddlewheeler boat, which brought new immigrants interested in farming the fertile land of the river valley. Today, the river maintains a major role in the transportation of goods by barge from Louisiana to Minnesota and elsewhere. The ecological nature of the river and its surroundings has changed profoundly through each of these phases.

Upper Mississippi River

The Upper Mississippi River begins at Lake Itasca, Minnesota, and flows south about 1,248 miles (2,008 kilometers) to join the Ohio River at Cairo, Illinois. This part of the river includes areas in Minnesota, South Dakota, Wisconsin, Illinois, Indiana, Iowa, and Missouri that drain water from a set of other major rivers: the Missouri, Ohio, Minnesota, St. Croix, Wisconsin, and Illinois. The Upper Mississippi flows through boreal forests, glacial lakes, sand plains, and bog and spruce swamps.

Forest composition in this segment includes paper birch, black spruce, jack pine, white pine, sugar maple, red maple, oak, and balsam fir. Evidence suggests that in the past, prairies and savannas may have been integral parts of these floodplain communities. However, in recent years, urban development, intensive agriculture, and fire suppression practices have led to the replacement of both prairie and savanna lands by flood-tolerant and fire-intolerant species.

The annual spring flood inundates the floodplain, which ranges from less than 1 to 6 miles (1 to 10 kilometers) wide here. This action changes the physical characteristics of the floodplain, along with islands, bank areas, and channels. This annual flood cycle is vital for nutrient cycling and for the reproduction of fish that are dependent on floodplain spawning habitats. The Upper Mississippi is rich in both invertebrate and vertebrate populations, with an estimated 430 taxa of invertebrates and 145 fish species inhabiting the river system. Endangered and threatened species of freshwater mussels found in the Mississippi River include the winged mapleleaf, Higgins’ eye pearly mussel, and fat pocketbook.

The most common fish species in the upper Mississippi River are the northern pike, common shiner, bluegill, bullhead minnow, largemouth bass, black crappie, channel catfish, white bass, river shiner, and emerald shiner. Several fish species are listed as endangered or threatened, including the skipjack herring, whose migratory path has been cut off by dam construction. Other vertebrates include eleven species of salamanders, fourteen types each of turtles and frogs, six kinds of snakes, and three species of mammals.

Because of its location, the Upper Mississippi River has been a center of commerce and civilization since prehistoric times. The river has been affected by human actions intended to alter the river for transportation and to irrigate the surrounding floodplain for agricultural and urban development. Major human effects include the construction of more than two dozen locks and dams. These dams have increased the sedimentation rate, decreased the quality of habitats, reduced the zones of primary production, and formed a large slow-flow area before the river reaches the next dam.

Agriculture in the floodplain is probably the most important water-quality issue in the river. It has led to increases in the concentration of nitrogen and phosphorus as the river flows to the confluence with the Ohio River. Similarly, the presence of nonnative species in the river has become an ecological concern. The common carp is one such species threatening native species in the river.

Lower Mississippi River

The Lower Mississippi River begins at Cairo, Illinois, and flows southward to Baton Rouge, Louisiana, before draining into the Gulf of Mexico. This part of the river basin drains from the Arkansas, White, Red, and Yazoo Rivers, and three distinct physiographic provinces: coastal plain, Ouachita province, and Ozark plateau. The coastal plain is large, with alluvial deposits; the Ouachita province is characterized by ridges and valleys; and the Ozark plateau consists of highlands composed of limestone, sandstones, and shales.

The basin area here covers 339,770 square miles (880,000 square kilometers) in Arkansas, Mississippi, Missouri, Louisiana, Tennessee, and Kentucky. This lower basin is highly productive land that has been cleared for growing soybeans, rice, cotton, and corn. Most of the agricultural land is maintained as cleared fields for row-crop farming. In addition, confined animal production facilities for poultry or swine are combined with pasture for beef production. Although the manure from the facilities is spread in the pasture, it contributes to nonpoint source (nondiscernible source) river pollution as organic matter.

The Lower Mississippi River is rich in biodiversity, and it is mostly forested, unlike the upper section of the river. The lower river contains parts of six terrestrial ecoregions: central US hardwood forests, Ozark mountain forests, Piney Woods forests, Southeastern mixed forests, Western Gulf Coastal grasslands, and Mississippi lowland forests. The forests are mainly composed of oaks, hickories, gums, hackberries, birches, loblolly pines, and willows. The floodplain of the lower Mississippi River is one of the largest in the world; it contains 13,900 square miles (36,000 square kilometers) of wetland habitats.

The channels of the river are abundant in several species of caddisflies, chironomids, oligochaetes, and clams. Some ninety-one species of fish have been reported, including channel catfish, common carp, freshwater drum, threadfin shad, smallmouth buffalo, blue catfish, yellow bullhead, minnows, and pirate perch.

Likewise, amphibians and reptiles are diverse and abundant, especially in the southern coastal zone. Species include American alligators, turtles (such as the common snapping turtle, red-eared turtle, and alligator snapping turtle), snakes (such as the diamondback water snake and western cottonmouth), and frogs (such as the bullfrog, pig frog, spring peeper, and cricket frog). Large animals include beavers, muskrats, raccoons, minks, river otters, white-tailed deer, swamp rabbits, black bears, and endangered red wolves. The majority of the fish and animal species are hunted and fished for their commercial value.

Human Impact

Human activities have extensively altered the physical, chemical, and biological integrity of the lower Mississippi River. The major sources of these alterations are engineering projects to improve navigation and control flooding; pollution from industrial, urban, and agricultural activities in 40 percent of the nation’s contiguous states; and the introduction of nonnative species.

With the advent of powerful boats, the Mississippi River became an important avenue for the transportation of materials from the North American heartland to the ports of Baton Rouge and New Orleans. Several dams and levees were constructed to maintain the flow of water for transportation. One such project involved reservoir and lock-and-dam construction on tributaries as part of the Mississippi River and Tributaries Project. In addition, the input of municipal wastes, sedimentation, industrial effluents, and agricultural runoff has created a dead zone downstream in the estuary and out into the Gulf of Mexico. It is estimated that the Mississippi River carries 331 to 550 million tons (300 to 499 million metric tons) of sediment past New Orleans each year.

Despite a long history of human activities, the upper part of the Mississippi River retains much of its natural condition, with more than 80 percent of the floodplain connected to the river, and its hydrology still resembles natural conditions. The point-source pollution was significantly reduced following the enactment of the Clean Water Act, the implementation of better industrial waste management, and improved sewage treatment around urban areas. However, various human activities have significantly altered the region. Infrastructure construction for transportation of materials and inefficient use of resources by communities have resulted in decreased biodiversity and led to severe flooding in recent years. Climate change is increasing the chance of flooding from shifting weather patterns and more severe storms and erosion, at the same time that it is extending and deepening drought effects on neighboring lands and applying stress to riverine habitats dependent on year-round moisture. The dead zone in the Gulf of Mexico and the accelerating rate of coastal wetland loss in Louisiana remain pressing environmental concerns that have immediate economic and human impacts.

In 2015, America's Watershed Initiative released the first-ever report card for the Mississippi River basin, which graded the watershed on six measures: water supply, marine transportation, flood control and risk reduction, economic impact, recreation, and ecosystem health. The average grade for the six measures for the entire Mississippi River basin was a D+, with marine transportation, water supply, and flood control and risk reduction receiving the lowest grades of all six parameters measured. In particular, infrastructure maintenance (one of the three components of marine transportation) received the lowest scores out of all parameters. The report highlighted a dangerous lack of funding for infrastructure maintenance and warned that continued deterioration of critical components for locks and dams could lead to severe economic losses, public safety hazards, and water security problems in the future. Failures in key infrastructure in the Mississippi River watershed would have a major economic impact, as the Mississippi River is used to transport approximately $54 billion of agricultural products each year, representing 92 percent of US farm exports. The America's Watershed Initiative released a second report card in 2020, raising the river's grade to a C-. The report card noted improvements in infrastructure but also indicated that the Mississippi River's water quality remains very poor.

In 2022, the state government announced plans to open part of a levee, which would divert some of the muddy river water into the bay. This will help rebuild the wetlands lost by sinking land and rising water levels caused by global warming. The two-billion-dollar project gained official approval from the US Army Corps of Engineers. Construction funding was approved in 2023. In 2025, Louisiana moved to terminate the Mid-Barataria Sediment Diversion Project. However, the project is controversial because the influx of freshwater may hamper the livelihoods of fishers who earn their living catching and selling oysters and shrimp. Nearby homeowners fear that the project will cause flooding, and environmentalists worry that it may harm bottlenose dolphins, which receive federal protection.

In 2024, the Mississippi River was recorded at an unusually low water level for the third year in a row. This forced barge companies to place limits on how much cargo their barges can transport, reducing farm profits and increasing costs.

Bibliography

Benke, Arthur C., and Colbert E. Cushing. Rivers of North America. Elsevier Academic Press, 2005.

“Louisiana Moves to Terminate Mid-Barataria Sediment Diversion Project.” NOAA Gulf Spill Restoration, 17 July 2025, www.gulfspillrestoration.noaa.gov/2025/07/louisiana-moves-terminate-mid-barataria-sediment-diversion-project. Accessed 9 Mar. 2026.

"Mississippi River Facts." National Park Service, 15 Feb. 2025, www.nps.gov/miss/riverfacts.htm. Accessed 7 Mar. 2026.

Morris, Christopher. The Big Muddy: An Environmental History of the Mississippi and Its Peoples from Hernando de Soto to Hurricane Katrina. Oxford UP, 2012.

Ruth, Maria Mudd. The Mississippi River. Benchmark, 2001.

Salter, Jim. "The Mississippi River Is Running Low Again. It's a Problem for Farmers Moving Beans and Grain." AP News, 11 Sept. 2024, apnews.com/article/mississippi-river-low-water-level-7dc8782f47fb7f0b6cb4e51528c10f3c. Accessed 7 Mar. 2026.

"The 2020 Mississippi River Watershed Report Card." America's Watershed Initiative, americaswatershed.org/reportcard/. Accessed 7 Mar. 2026.

Upholt, Boyce. "The Controversial Plan to Unleash the Mississippi River." Wired, 23 July 2022, www.wired.com/story/the-controversial-plan-to-unleash-the-mississippi-river/. Accessed 7 Mar. 2026.