Yes, the Mississippi River is polluted. Stretches of the river exceed water quality standards for mercury, bacteria, sediment, PCBs, and excess nutrients, according to the National Park Service. The pollution comes from a mix of agricultural runoff, industrial discharge, and urban stormwater, and it affects everything from local drinking water treatment to marine life hundreds of miles away in the Gulf of Mexico.
The Biggest Problem: Nutrient Runoff
The single largest pollution issue in the Mississippi River is excess nitrogen and phosphorus washing off farmland in the basin. The river drains about 40% of the continental United States, collecting fertilizer runoff from millions of acres of cropland across the Midwest. These nutrients fuel massive algae blooms that deplete oxygen in the water, harming fish and other aquatic life along the way.
The most dramatic consequence shows up at the river’s mouth. Every summer, all that nutrient-laden water empties into the Gulf of Mexico and creates a “dead zone,” an oxygen-starved area where fish and marine life can’t survive. In summer 2025, NOAA scientists measured the dead zone at approximately 4,402 square miles. While that’s the 15th smallest zone recorded in 39 years of measurement, it’s still an area roughly the size of Connecticut. The EPA maintains a dedicated Hypoxia Task Force focused on reducing nutrient loads, but progress has been slow given the sheer scale of the watershed.
Chemical Contaminants in the Water
Beyond nutrients, the river carries a cocktail of industrial chemicals. PFAS, the so-called “forever chemicals” used in nonstick coatings and firefighting foam, have been detected throughout the upper Mississippi basin. A study published in Environmental Science & Technology found that 94% of 177 water samples collected from the upper river had measurable PFAS levels. Most individual compounds were below 10 parts per trillion, but some hotspots near point sources showed concentrations as high as 458 parts per trillion for one common type, suggesting industrial or municipal discharge points along the river.
PCBs, legacy pesticides like DDT and toxaphene, and mercury also persist in the system. These chemicals were banned or restricted decades ago, but they break down slowly and accumulate in river sediments and fish tissue. The Mississippi Department of Health advises limiting consumption of certain fish caught in parts of the river and delta. For bass and large catfish from waters under mercury advisories, children under seven and women of childbearing age should eat no more than one meal every two months. Other adults are advised to limit those fish to one meal every two weeks. In some delta waters, carp, buffalo, gar, and large catfish carry enough DDT and toxaphene residue that all adults are advised to limit consumption to one meal every two weeks.
Heavy Metals in River Sediments
The riverbed itself tells a pollution story. U.S. Geological Survey sampling of 25 navigation pools in the upper Mississippi found elevated lead concentrations in several areas, with the highest levels in Lake Pepin (averaging 40 micrograms per gram of sediment) and notable concentrations in Pools 12, 19, and 26. The USGS describes Lake Pepin’s sediments as “moderately polluted” with lead. Mercury levels in Lake Pepin sediments exceeded the threshold known to increase mortality in fish embryos and larvae.
Industrial corridors along the river contribute to these deposits. The Illinois River near Hardin, Illinois, for example, showed lead concentrations roughly double those in neighboring stretches. While no federal health guidelines exist specifically for heavy metals in river sediments, these metals can work their way into the food chain through bottom-feeding fish and organisms that live in the mud.
Microplastics From Source to Sea
Microplastics are a newer concern, and the Mississippi carries plenty of them. Research from Johns Hopkins University found microplastics at every sampling site along the river, with an average of about 7 particles per liter and counts ranging from 2 to 14 particles per liter. These tiny fragments come from synthetic clothing fibers, degraded plastic packaging, tire wear, and industrial processes. They’re small enough to pass through many water treatment systems and are increasingly found in the tissue of river fish.
What This Means for Drinking Water
Roughly 18 million people rely on the Mississippi River as their drinking water source. Cities like New Orleans, Baton Rouge, St. Louis, and Minneapolis all draw water from the river or its immediate tributaries. Municipal treatment plants filter and disinfect this water before it reaches taps, and the finished product generally meets federal safety standards. But the treatment burden is significant. Utilities must remove or reduce nutrients, bacteria, sediment, and trace chemicals, and the presence of harder-to-treat contaminants like PFAS has raised concerns about whether current treatment technology is adequate everywhere along the river.
The pollution in the Mississippi isn’t one problem with one solution. It’s the accumulated runoff of an entire continent’s agriculture, industry, and urban life funneled into a single channel. Nutrient reduction strategies exist at the state and federal level, but the river’s condition reflects the reality that meaningful improvement requires changes across dozens of states and thousands of individual pollution sources spread across the basin.