Airborne mercury falls back to earth in precipitation, ending up in lakes.
Bacteria in lake sediment convert mercury into a form easily absorbed by fish and other organisms, including people who eat these fish. Studies have shown that mercury accumulation in fish-consuming wildlife may lead to reproductive problems. Human consumption of fish that contain mercury can damage the nervous system, especially in children and fetuses. The DNR has been conducting numerous studies about mercury in the environment and actively warning Wisconsin citizens about the risks of mercury since the 1970s. The DNR issues an annual fish consumption advisory offering people safe consumption guidance covering all inland Wisconsin waters.