Mercury in fish tissue

Toxic levels of mercury can pose a health concern for those who eat fish. Mercury found in fish tissue can also indicate that there might be a long-term source of mercury polluting a waterbody.

We look at the amount of mercury in edible tissue from freshwater fish to understand if contamination levels are changing. Large- and smallmouth bass are a resident species that can help us better understand long-term accumulations of mercury in rivers and lakes.

Each year, we collect 10 individual largemouth or smallmouth bass from six waterbodies to analyze total mercury accumulation. We return to each set of waterbodies every five years to assess trends. We monitor mercury because it persists in the environment, accumulates in the tissue of fish and humans, and is toxic in large concentrations.

We monitor mercury to protect health

Mercury is highly toxic and bioaccumulative, meaning that levels increase as it passes up aquatic food chains. This results in concentrations that can be harmful to fish-eating wildlife, such as birds of prey and humans. Because of these health issues, we worked with the state Department of Health to develop a Chemical Action Plan for mercury in 2003. The plan details natural and human-caused sources, identifies the way mercury moves through the environment, summarizes health effects, and how we issue fish consumption advisories.

Our long-term monitoring program has assessed mercury in fish tissue in support of the Chemical Action Plan since 2005. We monitor mercury levels in edible fillets of freshwater fish throughout Washington and compare the results over time to understand if fish tissue contamination levels are changing in response to cleanup efforts or other factors.

Latest full report

Measuring Mercury Trends in Freshwater Fish in Washington State - 2014 Sampling Results is our latest report from statewide monitoring. (Note that sample analysis and report preparation takes two to three years from time of sampling.)

See our data

Information gained from this project is useful in understanding what happens to mercury in our environment and provides the state Department of Health with data to offer guidance on which fish and how much fish can be safely eaten under specific circumstances.

Persistent, Bioaccumulative Toxics (PBTs) data in the Environmental Information Management system contains all our mercury in fish tissue data.

To see our reports, click on each monitoring location in the map.

Map-based Environmental Information Management database. Also find by searching EIM.