Most of those reservoirs appear like fantastic locations to launch a ship, however that is the issue. Anglers nonetheless pull bass and catfish from water that carries a do-not-eat order, and the hazard hardly ever reveals on the floor. It settles into the sediment and climbs into fish tissue as a substitute. There is no such thing as a federal rating of the nation’s most polluted reservoirs, so those under had been chosen from the arduous paper path: fish-consumption advisories, Clear Water Act listings, and Superfund data from the EPA, USGS, and state businesses. The contaminants run from PCBs and mercury to selenium, PFAS, and poisonous algae.

Lake Roosevelt, Washington

Lake Roosevelt extends about 151 miles behind Grand Coulee Dam and holds the higher Columbia River after it crosses the Canadian border. For a lot of the 20th century, a smelter in Path, British Columbia, discharged slag and different metallurgical wastes upstream. U.S. Geological Survey investigations detected elevated arsenic, cadmium, copper, lead, mercury, and zinc in reservoir sediment, water, or aquatic organisms. USGS described closely contaminated sediment in components of the system and measured concentrations able to harming bottom-dwelling organisms. Reservoir drawdowns expose broad bands of shoreline sediment, which prompted further USGS research of hint parts in materials that may dry and develop into airborne. EPA is conducting a Superfund remedial investigation throughout the Higher Columbia River and Lake Roosevelt space, overlaying sediment, seashores, fish tissue, and different potential pathways for human and ecological publicity.

Watts Bar Reservoir, Tennessee

Watts Bar Reservoir took in contaminants carried down the Clinch River from the Oak Ridge Reservation, the place nuclear and industrial operations launched mercury, PCBs, radionuclides, and different pollution. EPA data place 82 river miles of the Clinch River and its Watts Bar Reservoir arm throughout the space affected by Oak Ridge contamination.

USGS sediment-core research estimated that about 76 metric tons of mercury collected in Watts Bar sediment. Researchers additionally calculated that roughly 91 % of 335 curies of cesium-137 launched by Oak Ridge operations stayed in reservoir sediments. PCBs entered the river system as nicely and constructed up in fish.

Tennessee fish-consumption steering covers affected parts of Watts Bar and consists of restrictions for species reminiscent of catfish and striped bass. Federal research have discovered a lot of the historic mercury and radioactive materials buried in reservoir sediment, whereas PCB publicity continues to be managed by means of fish advisories.

Cottage Grove Reservoir, Oregon

Cottage Grove Reservoir lies downstream from Black Butte Mine, the place mercury mining contaminated the Coast Fork Willamette River watershed. Oregon issued a mercury-based fish-consumption advisory for the reservoir in 1979, the primary such advisory for a water physique within the state. Mercury reaching the reservoir can convert to methylmercury and construct up progressively in fish, significantly long-lived predators reminiscent of largemouth bass.

A 2025 Scientific Stories research examined fish collected throughout 2021 by means of 2023 and measured a median total-mercury focus of 0.710 micrograms per gram in 286 largemouth bass. The very best specimen contained 6.62 micrograms per gram, about 22 occasions EPA’s 0.3-microgram-per-gram fish-tissue criterion. Oregon Well being Authority steering tells kids and people who find themselves pregnant, might develop into pregnant, or are breastfeeding to keep away from resident fish from Cottage Grove. Consumption limits additionally apply to different adults, with separate suggestions for sure stocked rainbow trout.

Lake Hartwell, South Carolina and Georgia

Lake Hartwell took on PCB contamination by means of the Twelve Mile Creek watershed after the Sangamo Weston capacitor plant in Pickens, South Carolina, discharged PCB-bearing wastewater into City Creek. EPA data estimate that greater than 400,000 kilos of PCBs entered the creek system earlier than their use on the plant ended within the Seventies. The contamination led to the Sangamo Weston/Twelve Mile Creek/Lake Hartwell Superfund web site and years of sediment elimination and monitoring. South Carolina at present advises folks to eat no fish of any species from Twelve Mile Creek or the Seneca River arm of Lake Hartwell. Hybrid and striped bass caught in different South Carolina parts of the reservoir additionally carry a do-not-eat advice. Mercury provides one other concern, with state recommendation limiting consumption of largemouth and noticed bass in components of the lake. EPA continues sampling fish tissue and sediment for persistent contaminants.

Lahontan Reservoir, Nevada

Mercury entered the Carson River throughout nineteenth-century gold and silver processing, when mills used the metallic to get better treasured metals from ore. Waste mercury traveled downstream and settled into river and reservoir sediments, together with these at Lahontan Reservoir close to Fallon.

EPA consists of Lahontan throughout the Carson River Mercury Superfund Website and has reported extraordinarily elevated mercury concentrations in fish from the reservoir. Nevada and federal steering recommends no consumption of sport fish or carp caught there. EPA danger assessments have recognized issues for frequent customers, with explicit consideration to kids and being pregnant as a result of methylmercury can injury the creating nervous system.

Swimming, boating, and catch-and-release fishing are permitted at Lahontan. The consumption warning facilities on fish tissue, the place methylmercury concentrations rise because the chemical strikes by means of the meals net and builds up in bigger predatory fish.

Grand Lake St. Marys, Ohio

Grand Lake St. Marys takes in heavy nutrient a great deal of phosphorus and nitrogen, a lot of it carried into the shallow western Ohio reservoir by means of agricultural runoff. These vitamins feed dense cyanobacterial blooms able to producing microcystin, a liver toxin that may complicate recreation and drinking-water remedy.

Ohio EPA’s 2024 Built-in Water High quality Monitoring and Evaluation Report states that uncooked water on the Metropolis of Celina consumption exceeded the state’s microcystin threshold yearly starting with the beginning of monitoring in 2009 by means of the interval coated by the report. Exceedances occurred throughout each season in some years. The biggest focus cited by the state was 194 micrograms per liter in mid-Might 2017. A scientific evaluation overlaying 2009 by means of 2021 discovered a median weekly microcystin focus of 23.2 micrograms per liter, with measurements reaching 185 micrograms per liter.

Lake Koocanusa, Montana

Lake Koocanusa takes in selenium by means of the Elk River watershed in British Columbia, the place massive open-pit coal mines launch selenium into tributaries of the Kootenai River system. USGS monitoring has traced a lot of the reservoir’s selenium enter to the Elk River, although that tributary contributes a smaller portion of the mixed water flowing into the reservoir.

Montana designated Lake Koocanusa as threatened by rising selenium concentrations in 2012 and adopted a reservoir-specific dissolved selenium normal of 0.8 micrograms per liter in 2020. EPA authorized the usual in 2021. Regulators additionally use a fish-egg tissue normal of 15.1 milligrams per kilogram dry weight as a result of selenium accumulates in aquatic meals webs and may intervene with fish copy. USGS monitoring covers water, aquatic bugs, fish tissue, and fish eggs, with explicit consideration to deformities and diminished survival throughout early growth.

Lake Nacimiento, California

Lake Nacimiento in San Luis Obispo County seems on California’s Clear Water Act impaired-waters record for mercury. State fish-consumption recommendation rests on tissue measurements exhibiting elevated concentrations in a number of species generally caught by anglers.

California’s Workplace of Environmental Well being Hazard Evaluation reported common mercury concentrations of about 1.01 components per million in black bass and 1.15 components per million in white bass within the dataset used to arrange its steering. Girls ages 18 by means of 49 and youngsters ages 1 by means of 17 are suggested to eat no black bass, channel catfish, frequent carp, crappie, or white bass from Nacimiento. California’s 2026 Built-in Report additionally consists of fish-tissue proof above the 0.3-microgram-per-gram mercury guideline used within the state’s evaluation. Separate serving suggestions apply to species with decrease measured mercury concentrations, which makes species identification vital earlier than an angler retains fish for a meal.

Brier Creek Reservoir, North Carolina

Brier Creek Reservoir lies downstream from the Ward Transformer Superfund web site close to Raleigh, the place transformer operations launched PCBs into soil, drainage channels, streams, sediment, and fish. EPA investigations traced PCB contamination by means of the drainage system into Brier Creek Reservoir, and North Carolina issued a do-not-eat advisory overlaying all fish caught there. EPA accomplished main downstream contaminated-sediment elimination in 2023 after which continued long-term fish-tissue monitoring. The cleanup goal requires PCB concentrations in fish from Brier Creek Reservoir and close by Lake Crabtree to fall under 0.05 milligrams per kilogram. EPA has estimated that reaching that focus may take about 15 years as a result of PCBs already labored into aquatic meals webs decline slowly after contaminated sediment is eliminated. Fish sampling is predicted to proceed for a decade or longer whereas concentrations are tracked in opposition to the federal cleanup goal.

Monee Reservoir, Illinois

Illinois positioned Monee Reservoir in Will County beneath a fish-consumption advisory after testing detected elevated PFOS in largemouth bass. PFOS belongs to the PFAS household of fluorinated chemical substances, which resist environmental degradation and may construct up in edible fish tissue.

Present Illinois steering tells anglers to eat no largemouth bass from Monee Reservoir due to PFOS measured in fillets. The advisory applies to consumption of that species and doesn’t shut the reservoir to boating or different leisure use.

Illinois EPA has expanded PFAS sampling by means of its Fish Contaminant Monitoring Program because the state measures these chemical substances in freshwater fish. Sampling focuses on edible fillet tissue, the portion used to calculate consumption recommendation. Outcomes from Monee had been excessive sufficient for the state to difficulty its no-consumption advice for largemouth bass, including PFOS to the reservoir pollution now tracked alongside older contaminants reminiscent of mercury and PCBs.

Donna Reservoir, Texas

Donna Reservoir and its canal system close to the Rio Grande turned a federal Superfund web site after PCBs had been detected in fish in 1993. Texas prohibited the taking of aquatic life from the location, and EPA warning indicators inform anglers that possessing fish caught there’s unlawful. Investigations discovered PCBs in sediment and fish tissue, with consuming contaminated fish recognized because the principal human publicity route. EPA excavated greater than 24,788 tons of contaminated sediment throughout a cleanup accomplished in 2020.

The issue didn’t disappear with the dredging. EPA’s 2024 5-Yr Evaluate discovered that the cleanup was not but protecting as a result of PCB concentrations in fish remained above remediation targets and other people continued eradicating fish for potential consumption. The company labeled human publicity by means of fish consumption as uncontrolled on the web site. Sampling and enforcement due to this fact proceed a long time after PCBs had been first detected within the reservoir.

Spring Creek Reservoir, California

Spring Creek Reservoir close to Redding was constructed to manage contaminated drainage from the Iron Mountain Mine space earlier than releases attain Keswick Reservoir and the Sacramento River. Water draining the mine comprises exceptionally excessive concentrations of metals and excessive acidity. USGS measured pH values as little as -3.6 in Iron Mountain drainage and documented copper, cadmium, zinc, iron, aluminum, lead, and different parts. Sampling of Spring Creek Reservoir effluent additionally discovered elevated concentrations of a number of metals. Federal remedy and source-control initiatives have reduce copper and zinc releases from Iron Mountain by roughly 80 to 90 % for the reason that mid-Nineteen Nineties, based on USGS. Operators use Spring Creek Reservoir to carry and regulate acidic drainage so releases may be timed and diluted earlier than they attain the Sacramento River system. EPA positioned Iron Mountain Mine on the Nationwide Priorities Record in 1983 and has carried out a number of cleanup actions throughout the location.

Studying a Reservoir’s Paper Path

What ties these reservoirs collectively will not be a single pollutant however a sample: a legacy business upstream, a contaminant that settles into sediment and climbs into fish, and a monitoring program that outlives the operation that triggered the issue. Donna, Lake Hartwell, and Brier Creek hint again to PCB-handling vegetation; Lahontan and Cottage Grove to mercury-era mining; Spring Creek to acid drainage nonetheless being neutralized a long time later; Koocanusa and Grand Lake St. Marys to air pollution that crosses a border or a property line and arrives as another person’s runoff. Typically the water stays open for boating and swimming whereas the warning lives on the fish. That hole, between a reservoir that appears fantastic and a fillet that fails a well being benchmark, is the rationale these advisories exist and the rationale sampling continues 12 months after 12 months.