Pristine Lakes, Poisoned Fish

MPR News recently explored a growing environmental and public health concern in Minnesota in the article Across northern Minnesota’s pristine lake country, mercury contamination is growing (Kraker, 2025). Known for its pristine wilderness and lakes, northern Minnesota contains hundreds of lakes rendered unsafe because of elevated mercury levels in fish. Mercury is highly toxic to humans, and exposure can cause neurological issues such as slurred speech and tremors. Fetuses and children younger than fifteen are especially vulnerable to mercury, which can result in long-term impairments in cognition, memory, language, and learning ability.

Since 2005, Minnesota has reduced the amount of mercury released into the atmosphere by two-thirds. However, the state will not meet its 20-year goal of a 93 percent reduction from 1990 levels by this year, and the mercury levels in fish continue to increase. Tests showed that 80 percent of sampled walleye and northern pike contained mercury levels above the safety threshold for consumption.

Scientists identify several interacting causes behind rising mercury levels in Minnesota fish, including climate change, invasive species, and sulfate released into waterways by mining and other industries. Although mercury is naturally released from volcanoes and forest fires, multiple anthropogenic pollutants contribute to the problem in Minnesota. A major local source of mercury contamination is the region’s taconite plants, combined with atmospheric deposition from fossil fuel facilities, gold mines, and other industrial activities.

What happens to mercury once it enters the lakes and rivers makes the problem even more complex. Mercury builds up in fish at concentrations far higher than in surrounding water. Northern Minnesota’s wetlands and nutrient-poor lakes create ideal conditions for toxic accumulation of mercury. Top predators like walleye often exceed safe consumption limits due to slower growth and longer lifespans. The problem is intensified by sulfate pollution, invasive species such as zebra mussels, and climate change - all of which accelerate the toxic effect of mercury.

The most effective solution is to reduce the mercury entering the environment where it accumulates in the food chain. Scientists remain hopeful that biotechnology tools can help advance progress on this issue. Meanwhile, these risks are not shared equally. The issue is particularly serious for local Native American communities that rely on subsistence fishing both for nutrition and for maintaining cultural traditional practices. A 2011 study found that 10 percent of local newborns had mercury levels exceeding the safety threshold.

Reference

Kraker, D. (2025, August 5). Across northern Minnesota’s pristine lake country, mercury contamination is growing. MPR News. Updated August 13, 2025.

https://www.mprnews.org/story/2025/08/05/mercury-pollution-minnesota-lake-country