What Is Mercury?
Mercury is a hazardous chemical that occurs naturally in the environment and is also used in various industrial applications.
How Does Mercury Get Into Freshwater Fish?
In lakes and other freshwater bodies, small organisms convert naturally occurring inorganic mercury into its organic form, methylmercury. Methylmercury binds with particles and sediments that are consumed by smaller fish. Larger game fish prey on these smaller, mercury-contaminated fish. Because fish eliminate mercury very slowly, it accumulates in their tissues and organs. Unlike some organic contaminants that concentrate in the skin and fat, mercury cannot be removed by filleting or cooking.
How Do We Know the Extent of the Problem in South Dakota?
Each year, South Dakota samples at least 10 lakes for a panel of 25 contaminants, including mercury. Before the current state testing program began, only one water body in the state had been found to exceed the FDA’s action level of 1 ppm. That advisory was issued in 1974 for the Cheyenne River, where mercury contamination was traced to mining activity in the Black Hills.
This testing is a joint effort by the South Dakota Department of Game, Fish and Parks, the South Dakota Department of Agriculture and Natural Resources, and the South Dakota Department of Health.
How Concerned Should I Be About Mercury Exposure From Eating Freshwater Fish?
For the most current guidance on mercury in fish, we recommend reviewing the FDA’s “Advice About Eating Fish” handout. This easy-to-understand resource helps you choose safe and healthy fish options for yourself and your family, including recommendations for children and those who are pregnant or breastfeeding.
Is Mercury a Risk From Swimming or Other Recreational Activities in Freshwater?
No. There is no known health risk from mercury exposure related to swimming, boating, or catch-and-release fishing. While mercury levels may be elevated in fish, the chemical concentration in the water is typically up to 100,000 times lower. Handling fish is highly unlikely to expose someone to harmful levels of mercury.
Do Other States Test for Mercury and Issue Consumption Advisories?
Yes. Many states test freshwater fish for mercury contamination. According to the EPA, all 50 states have issued fish consumption advisories. South Dakota’s neighboring states—Minnesota, North Dakota, Nebraska, and Montana—have all issued mercury-related advisories in the past.