Pollution of the Mississippi River

• IDENTIFICATION: Major inland tributary with headwaters at Lake Itasca in northern Minnesota, running south through ten US states to a delta below New Orleans, Louisiana

The second-longest river in the United States, the Mississippi serves as the drainage basin for a little more than 40 percent of the country, supplies drinking water to 20 million people, and is the principal route for inland waterborne commerce in the nation; one in twelve people across the globe consume products transported on the Mississippi River. Efforts to control its flow to accommodate commercial interests have created significant environmental problems that have adversely affected ecosystems and human communities along its banks.

The Mississippi River flows irregularly for approximately 3,750 kilometers (2,330 miles) through the midsection of the United States. It is fed by more than one hundred tributaries, including the Missouri and Ohio rivers. The Upper Mississippi, the region between the headwaters in Minnesota and the area in Illinois and Missouri where its two major tributaries join, is fairly narrow and shallow, at many points running between high bluffs. By contrast, the Lower Mississippi, shaped by activity during the Pleistocene glacial advance, is wide and deep. It runs through an alluvial floodplain that, before human intervention, frequently flooded in the spring.

The Mississippi River has been home to thousands of life-forms, including several endangered species; hundreds of bird species and mammals populate its shorelines. It is the most important bird and waterfowl migration route in North America. Its bottomlands are the largest wetland area and support the largest hardwood forest in the United States. Since the nineteenth century, however, engineering projects undertaken to benefit commercial enterprises have caused serious degradation of the Mississippi as a site for balanced natural ecosystems. Major damage has occurred principally in two forms: pollution introduced directly from commercial enterprises or indirectly by projects designed to control the flow of the river for commercial or recreational purposes, and flooding exacerbated by efforts to channel the river to maintain optimal shipping lanes.

Commercialization and Its Impacts

Since the nineteenth century, the Mississippi River has served as a major route for commerce traveling from America’s heartland to the Gulf of Mexico (Gulf of America) and from there to locations around the world. Numerous commercial enterprises and ports sprang up along the river during the nineteenth century, and farming became a major activity all along the Mississippi; in the lower regions, farms and plantations in the rich bottomlands took away natural habitats for wildlife, weakened the riverbanks through erosion, and diminished natural cover for the soil.

Charged with managing the nation’s waterways, the US Army Corps of Engineers began improving navigability on the Mississippi in 1879. Over the years, the Corps has undertaken a number of engineering projects to optimize the river’s value for commerce. After a disastrous flood in 1927, the Corps initiated several programs aimed at flood control. A series of twenty-seven locks and dams was constructed to create a continuous nine-foot shipping lane from Minneapolis to St. Louis, Missouri, guaranteeing the easy passage of barge traffic. Large earth-and-concrete levees were constructed to prevent flooding below St. Louis. In addition to flood prevention, the levees were designed to increase the force of the water to maintain a deep channel in the river. Nevertheless, for decades, the Corps has been forced to conduct systematic dredging, especially near the delta, where silt buildup makes it difficult for larger ships to travel into and out of the Gulf of Mexico.

These initiatives allowed commercial use of the river to increase dramatically; for example, in 2022, more than 589 million tons of cargo moved down the river. Farm crops make up the majority of this cargo, and farmers’ ability to use the river to send goods to ports around the country and the world has kept down the need for overland transport. Another twentieth-century development was the construction of paper mills, chemical plants, and oil refineries along the river’s banks, which proved an ideal location for companies wishing to ship large quantities of their products. Petroleum, petroleum products, and chemical products also make up cargo shipped on the Mississippi River network.

Pollution Problems

The benefits of commercial use of the Mississippi have been balanced, and perhaps outweighed, by damage done to the river’s ecosystems. Numerous species of fish and wildlife disappeared from the upper river as pools and backwaters between dams became silted. The high levees below St. Louis caused wetlands adjacent to the river to dry up, eliminating habitat for numerous species. Cities and towns have often dumped sewage into the river, and chemical runoff from farms, particularly phosphorus and nitrogen, has polluted the waterway from its northernmost reaches down to the Gulf. As far north as Minnesota, chemical plants have dumped toxic waste into the Mississippi, polluting it with a variety of toxins, including furan, trichlorobenzene, dichloro-diphenyl-trichloroethane (DDT), trichloroethane (TCA), and polychlorinated biphenyls (PCBs). The problem has become exacerbated farther south, especially from Baton Rouge, Louisiana, to the mouth of the river, where chemical plants and oil refineries are concentrated. The cumulative effects of toxic waste disposal, oil spillage, and other forms of refuse dumping have materially degraded the use of the river and its banks for fishing, hunting, and trapping and have led to the creation of a hypoxic (depleted of oxygen) area, known as a dead zone, at the mouth of the river extending into the Gulf of Mexico. This area is one of the largest dead zones in the world.

Until the 1960s, many commercial enterprises used the river as a dumping ground for waste, and little was done to protect the natural environment. Since the 1960s, however, environmental groups such as the Izaak Walton League and Greenpeace, as well as organizations sponsoring recreational use of the river, have been increasingly active in demanding that the federal government take measures to protect the Mississippi’s ecosystems. Their efforts have sparked modest programs to reduce pollution and reverse the adverse environmental effects of the levees, locks, and dams. A government-sponsored environmental management plan implemented in 1986 is aimed at restoring wetlands. Monitoring by the government and private groups has resulted in a reduction in point source pollution (that is, pollution caused by specific sources, such as refuse dumped by a specific business or city), but nonpoint source pollution, especially runoff from agricultural regions, has been much harder to control. In 2024, US State Representative Betty McCullum from Minnesota and Senator Tammy Baldwin from Wisconsin, introduced the Mississippi River Restoration and Resilience Initiative (MRRRI) to Congress. This piece of legislation was based on the successful Great Lakes Restoration Initiative (GLRI) and aimed to provide federal funding, operating within the Environmental Protection Agency, to states along the Mississippi River to combat environmental concerns.

Flooding and Flood Control

Traditionally, spring runoff from as far away as the Rocky Mountains to the west and the Appalachians to the east has caused the Mississippi River to rise above its banks and flood adjacent lands. The natural environment historically benefited from this seasonal event, as flooding created rich alluvial soil and wetland habitats. Efforts to control the flow of the Mississippi changed flood patterns significantly, however, as the river was hemmed in by high levees. Waters rushing downstream now do so more rapidly until, in extreme cases, their power creates levee breaks. Debris from the natural landscape and human structures swept away by the current and pollutants being carried downstream have wreaked havoc in flooded areas, and attendant damages to residential and commercial centers built up along the river have often run into the billions of dollars. In turn, the Army Corps of Engineers has been called upon to devise more stringent measures to keep the river within manageable boundaries, further reducing the wetland environments along the banks and concentrating pollutants within the river’s main channel. The Corps has also been active in implementing measures to keep the Mississippi from changing its main channel, a phenomenon common before the nineteenth century. Such changes could cause cities and towns along the river to become landlocked, which would materially affect their commerce.

Efforts to control flooding while maximizing the river’s commercial potential have also had negative effects downstream, especially around New Orleans. In 1965, the Corps created the Mississippi River Gulf Outlet (MRGO), a direct channel giving commercial ships a shorter route from the city to the Gulf of Mexico. The channel had little impact on reducing ship traffic, but its presence led to considerable erosion of marshes and wetlands south of the city. The impact was most noticeable when Hurricane Katrina hit in 2005. While the levees along the Mississippi were not breached, the surge from the Gulf traveled up the MRGO and over terrain bereft of natural barriers, causing breaches in flood walls of canals leading off the river into urban areas. Waters inundated New Orleans, creating one of the worst natural disasters in the history of the United States. The MRGO was permanently closed in 2009.

In 2016, the Friends of the Mississippi River and the National Park Service’s Mississippi National River and Recreation Area released the State of the River Report 2016, which reported assessments of the river’s flow; swimming and recreation; river life, including invasive Asian carp, bald eagles, and mussels; and ecological health, including data regarding contaminants. The report made the following conclusions and recommendations: the river is impaired by excess sediment, bacteria, and phosphorous; pesticide and chloride levels meet established standards but should be monitored; fish consumption guidelines have been issued because of elevated levels of contaminants such as mercury and perfluorooctanoic acid (PFOS); nitrate concentrations have increased; and microplastics, pharmaceuticals, and dioxins pose uncertain risks, which require additional research and mitigation. This was the second edition of the report, which highlighted fourteen indicators of Mississippi River health and explained them in a way that made the information accessible to non-scientists and the general public.

In 2022 and 2023, droughts decreased the river's water levels to historic lows, causing issues with barge traffic. The US Army Corps of Engineers began dredging the river in 2023 to ensure future droughts would not cause shipping delays. By the mid-2020s, pollution, habitat loss, flooding in some areas, and lower water levels in others continued to be the most pressing issues affecting the Mississippi River. However, microplastics and PFAS (per- and polyfluoroalkyl substances), also called forever chemicals, also became significant areas of concern. In April 2025, American Rivers listed the Mississippi River as the nation's most endangered river. In this declaration, experts cited mining pollution, aging infrastructure, and agricultural pollution, among other issues.

Bibliography

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