Mercury contamination in hundreds of northern Minnesota lakes is increasing, driven by a mix of industrial emissions, climate change, invasive species, and other factors that put fish and human health at risk even in protected wilderness areas.
Dan Kraker reports for MPR News.
In short:
- Mercury in walleye and northern pike in many northern Minnesota lakes now exceeds safe consumption limits, with some fish testing three to seven times over thresholds.
- Factors fueling the rise include sulfate pollution from iron mining, zebra mussel infestations, wetland-driven methylation, and climate change.
- University of Minnesota scientists are testing genetically engineered minnows designed to reduce mercury in the fish that eat them, though the approach remains experimental.
Key quote:
“Walleye are mercury magnets. Those types of game fish that are really up at the top of the food chain have the highest concentrations, and they’re often above limits that are safe for consumption.”
— Charles Driscoll, professor at Syracuse University
Why this matters:
Mercury is a potent neurotoxin that accumulates in fish and poses serious risks to human health, especially for fetuses and children, impairing brain development, memory, and learning. In northern Minnesota, the problem strikes at both cultural traditions and food security, particularly for Indigenous communities that rely on subsistence fishing. Once in the environment, mercury can cycle for decades, with wetlands, warming waters, and invasive species amplifying its toxicity. Because most mercury in these lakes comes from far beyond state borders, local cleanup efforts have limited effect. The result is a slow-moving but persistent contamination of ecosystems that otherwise appear pristine, undermining trust in the safety of wild foods and highlighting the long reach of industrial pollution.
Related: Dead fish carry toxic mercury to the deep ocean, contaminating crustaceans
