What is the most unhealthy freshwater fish to eat?

January 12, 2026 •

4 min read

According to the Environmental Working Group, consuming a single serving of freshwater fish can expose a person to the same level of 'forever chemicals' (PFAS) as drinking contaminated water for a month. Understanding this risk is crucial when considering which freshwater fish are the most unhealthy to eat due to accumulated toxins.

Quick Summary

Several freshwater fish species, including certain types of catfish, bass, and farmed tilapia, are considered unhealthy due to high concentrations of persistent pollutants like mercury, PCBs, and PFAS. These toxins, which bioaccumulate in fish, can pose significant health risks to consumers. Factors like feeding habits, water quality, and farming practices all influence a fish's contamination level.

Key Points

PFAS Contamination: A single serving of wild-caught freshwater fish can expose you to 'forever chemical' (PFAS) levels equivalent to a month of contaminated drinking water.
Mercury Accumulation: Predatory freshwater fish like bass and pike have higher levels of methylmercury, a potent neurotoxin.
Risks of Farmed Fish: Imported farmed species, particularly tilapia and certain catfish, can carry high levels of antibiotics, dioxins, and harmful bacteria due to poor sanitation.
Vulnerable Consumers: Pregnant women, nursing mothers, and young children are particularly susceptible to the harmful effects of contaminants like mercury and PCBs.
Partial Reduction of Contaminants: For fat-soluble pollutants like PCBs, proper trimming and cooking methods can reduce exposure, but this is ineffective against mercury.
Local Advisories are Key: Always check local fish consumption advisories for specific waterway warnings, as contamination levels vary significantly by location.

Understanding Contaminants in Freshwater Fish

While fish is generally a healthy source of protein and omega-3 fatty acids, freshwater varieties can pose unique health risks due to bioaccumulation of environmental toxins. Industrial waste, agricultural runoff, and atmospheric deposition introduce pollutants like mercury, Polychlorinated Biphenyls (PCBs), and Per- and Polyfluoroalkyl Substances (PFAS) into rivers and lakes. These substances accumulate in fish over their lifetime, particularly in larger, older, and bottom-feeding species.

The Rise of Concern Over Forever Chemicals (PFAS)

Recent research by the Environmental Working Group (EWG) highlighted a startling concern regarding 'forever chemicals' (PFAS) in freshwater fish. The median levels of PFAS in wild-caught freshwater fish were found to be 280 times higher than those in commercially sold seafood. A single annual serving of freshwater fish was equated to consuming a month's worth of drinking water contaminated with PFOS at levels considered harmful by advisory limits. This finding elevates PFAS as a significant and widespread threat in freshwater fish, especially for local anglers and communities dependent on freshwater fishing.

Mercury and PCBs: Lingering Threats

Mercury poisoning is a well-known risk associated with fish consumption, and freshwater species are not immune. Predatory freshwater fish like lake trout and pike accumulate high levels of methylmercury, a neurotoxin dangerous to developing brains in fetuses and young children. Similarly, PCBs, banned since 1979 but highly persistent in the environment, settle in waterway sediments. Bottom-dwelling species are particularly susceptible to absorbing these chemicals, which are linked to a range of health issues, including cancer, immune system dysfunction, and developmental problems.

The Most Unhealthy Freshwater Fish

Several freshwater species consistently appear on lists of fish to limit or avoid due to their high contaminant loads. These include:

Farmed Tilapia: Often raised in crowded, unsanitary conditions, imported farmed tilapia has been flagged for containing higher levels of contaminants like dioxin, antibiotics, and harmful bacteria compared to wild-caught varieties. The high omega-6 fatty acid content in farmed tilapia can also contribute to inflammation when consumed excessively.
Certain Catfish: Both wild-caught and certain imported catfish, particularly swai or basa from Vietnam, have been cited for contamination risks. Wild-caught bottom-feeding catfish can absorb toxins from sediment. Imported varieties have been found to contain illegal antibiotics and bacteria.
Largemouth Bass: As a top predator in the freshwater ecosystem, largemouth bass is prone to accumulating higher levels of pollutants like mercury and PFAS through biomagnification.
Freshwater Eels: Eels are known to have high levels of mercury and other persistent organic pollutants (POPs), including PCBs. Their long lifespan contributes to higher contaminant build-up.

Farmed vs. Wild-Caught: A Contaminant Comparison


Feature	Wild-Caught Freshwater Fish	Farmed Freshwater Fish
Contaminant Source	High levels of toxins from polluted rivers, lakes, and sediments.	Contaminants from unsanitary farming conditions and feed, often including antibiotics and chemicals.
Omega-3s vs. Omega-6s	Generally higher levels of healthy omega-3 fatty acids from natural diet.	High-fat, corn/soy-based feed leads to a less favorable ratio, with higher inflammatory omega-6s.
Exposure Risk	Varies by waterway and species; top predators pose higher risk.	Dependent on farming practices and country of origin; concerns over illegal antibiotics and dioxins exist.
Diet	Diverse, natural diet of aquatic life, influencing nutrient profile.	Monotonous, processed feed designed for rapid growth.

The Risks of Consuming Contaminated Fish

Consuming fish laden with contaminants poses numerous health risks that can affect various bodily systems. The effects vary depending on the specific toxin and the level of exposure. Risks include neurological damage, kidney damage, endocrine disruption, and an increased risk of cancer. Certain groups are especially vulnerable, including pregnant women, nursing mothers, and young children, as toxins like methylmercury and PCBs can harm the developing nervous system.

Preparing Fish to Reduce Contaminants

For some fat-soluble contaminants like PCBs, careful preparation can help reduce exposure.

Trim Away Fat: Since PCBs accumulate in the fatty tissues of fish, trimming off the skin, belly fat, and dark fatty meat can reduce the level of these contaminants.
Cook on a Rack: Cooking methods like grilling or broiling on a rack allows fat to drip away from the fillet, further minimizing fat-soluble pollutants.
Discard the Drippings: Never use the fat or juices for sauces, as this would reintroduce the contaminants you just removed.

It is important to note that these preparation methods do not reduce mercury levels, as mercury is stored throughout the fish's muscle tissue. For mercury-contaminated fish, the only safe option is to avoid consumption.

Conclusion: Making Smarter Choices

While fish offers undeniable health benefits, navigating the world of freshwater fish requires careful consideration due to widespread contamination risks. What is the most unhealthy freshwater fish to eat depends heavily on factors like its position in the food chain (top predators like bass) and its environment (polluted waterways, unsanitary fish farms). To minimize your risk, prioritize fish from clean sources and opt for smaller, wild-caught species. Always consult local fish advisories from environmental and health agencies before eating fish caught recreationally. By staying informed and making intentional choices, you can enjoy the benefits of fish while safeguarding your health from harmful pollutants. For further guidance on seafood, consult resources like the Monterey Bay Aquarium Seafood Watch list.

Frequently Asked Questions

Predatory freshwater fish, such as larger lake trout and pike, typically have the highest mercury levels. Mercury bioaccumulates up the food chain, so larger, older fish that eat other fish contain more concentrated toxins.

Yes, imported farmed tilapia is often considered unhealthy due to unsanitary and crowded conditions in some fish farms, which can lead to contamination with antibiotics, pesticides, and dioxins. A natural diet is not possible for fish that are raised on a processed diet.

'Forever chemicals' or PFAS are persistent man-made compounds that do not break down in the environment or the human body. They are found in high concentrations in freshwater fish and can accumulate in humans, posing risks like immune suppression, higher cholesterol, and potential cancer links.

No, cooking does not remove contaminants like mercury or PFAS, which are absorbed into the fish's muscle tissue. While trimming fat and broiling can reduce fat-soluble chemicals like PCBs, it is ineffective against mercury and other persistent pollutants.

Bottom-feeding fish, like some catfish, are more likely to absorb PCBs and other contaminants that settle in the sediment of polluted waterways. In areas with industrial runoff, these fish can accumulate high levels of harmful chemicals.

Pregnant women, nursing mothers, young children, and regular consumers of local catch are most at risk. Developing nervous systems are particularly vulnerable to neurotoxins like methylmercury and PCBs.

Not necessarily. While often better than poorly farmed varieties, wild-caught freshwater fish still face significant contamination risks from polluted waterways, including high levels of mercury and PFAS, depending on the local environment.