Mercury found in fish within our national parks

Staff writerMay 25, 2014 

This brook trout was one of the fish sampled at Mount Rainier National Park during a four-year study of mercury levels in fish within national parks. The results were released last month.


Mercury has been found in fish within the three national parks in Washington. In only one case, in Olympic National Park, did the level approach levels unsafe for humans.

These were among the findings released last month in a report from the U.S. Geological Survey and the National Park Service.

While Mount Rainier, North Cascades and Olympic national parks are not considered prime fishing destinations, the report’s finding should be fairly good news for recreational anglers.

The study was the first of its kind to incorporate information from remote places at 21 national parks in 10 western states. From 2008-2012, researchers sampled 1,486 fish from 16 species from 86 individual sites in the parks.

Western parks were selected because of the significant role atmospheric mercury plays in remote places, and the lack of broad-scale assessments on mercury in fish in remote areas of the West, said Colleen Flanagan Pritz, a Park Service ecologist in Denver and coauthor of the study.

At Mount Rainier fish were sampled from 17 lakes, ponds and wetlands, Flanagan Pritz said. The sites included Green, Mowich, Tipsoo and Reflection lakes, as well as the Nisqually River watershed. Researchers took samples from rainbow, cutthroat and brook trout, as well as kokanee, torrent sculpin and three-spined sticklebacks.

Among the Rainier findings, researchers found an 11-fold difference between the sites with the lowest and highest total mercury concentrations, according to the report. That was the highest among all the parks.

Despite the high range of mercury levels, “Mount Rainier was not one of those particular areas that exceeded the (human) benchmarks,” Flanagan Pritz said. “But there were benchmarks that were exceed for fish-eating birds at Mount Rainier.”

Hoh Lake in Olympic National Park was the one spot in the state’s national parks where the study found fish “are likely to approach or exceed the Environmental Protection Agency criterion for protection of human health and the avian benchmark for reproductive impairment.”

Size-adjusted concentrations at Hoh Lake were 253 nanograms per gram wet weight. The U.S. Environmental Protection Agency’s human risk threshold is 300 ng/g ww.

Overall, mercury concentrations were below EPA’s fish tissue criterion for safe human consumption in 96 percent of the sport fish sampled. Researchers were looking at how the samples related to benchmarks for fish, fish-eating birds and humans.

Among the most widespread contaminants in the world, mercury is distributed globally from natural sources such as volcanic eruptions and from human sources such as burning fossil fuels in power plants. Mercury is distributed at local or regional scales as a result of current and historic mining activities, the report said. These human activities have increased levels of atmospheric mercury at least threefold during the past 150 years, the researchers wrote.

Mercury, whether naturally occurring or in pollution, easily enters the food chain. When the metal enters the water or soil, it is naturally converted to methylymercury by bacteria. In water, that bacteria is eaten by plankton and other small creatures, which in turn are eaten by small fish, then larger fish.

“Mercury increases in concentration as it moves up the food chain,” Flanagan Pritz said. “The birds that eat fish will have more mercury in them than the individual fish they eat. The same for humans.”

According to the Centers for Disease Control and Prevention, exposure to high levels of mercury in humans can damage the brain, kidneys and a developing fetus. Pregnant women and young children are particularly sensitive to mercury.

In birds that eat fish, the effects of mercury can range from reduced nest success rates – a bird might not return to a nest to incubate its eggs – and reduced ability to forage. In fish, there are levels where changes in behavior are noticed, while higher levels could be lethal.

While previous studies documented mercury at Mount Rainier and other places in the West, this latest study “is a wake-up call,” Flanagan Pritz said.

“We need to see fewer contaminants in park ecosystems, especially contaminants like mercury where concentrations in fish challenge the very mission of the national parks to leave wild life unimpaired for future generations.”


North Cascades

There were three sites sampled and results should the mean mercury concentration was below the average of all fish sampled in the study. After standardizing the fish to 200 mm in length, the mean mercury concentration was 73.3 nanograms per gram wet weight.

Entire report

You can read the U.S. Geological Survey and National Park Service report at

Mount Rainier

Fish were sampled at 17 sites. The average mercury concentration was 71.5 ng/g ww, similar to the studywide mean for all the fish in the study. When adjusted to the 200 mm standardized size, concentrations ranged from 8.5-193.2 ng/g ww. That large variation “emphasizes the need to sample from multiple locations in order to accurately characterize mercury risk to park resources as a whole,” the report said.


Samples were take from five lakes, with concentrations averaging 85 ng/g ww, slightly higher than the mean for the study. Of note was Hoh Lake, where the size adjusted concentration was 253 ng/g ww. At the low end of the spectrum was Gladys Lake, with a concentration of 71.5 ng/g ww. “Our models of mercury risk to consumers reflects these higher concentrations and suggest that fish in Hoh Lake are likely to approach or exceed the EPA criterion for protection of human health and the avian benchmark for reproductive impairment above 180 mm,” said the report.

Sources: National Park Service, U.S. Geological Survey
Jeffrey P. Mayor: 253-597-8640

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