Mercury discovered in Lake Aaron fish: Pollution source hard to pinpoint
MILLERVILLE, Minn. — Lake Aaron near Millerville northwest of Alexandria is polluted and people should monitor how much fish they eat from it, state scientists say.
State scientists propose adding Lake Aaron to its list of impaired waters and the state will likely issue a fish consumption advisory after fish there tested positive for mercury at more than double what is considered safe.
The finding did not shock state Department of Natural Resources area fisheries supervisor Dean Beck.
"Virtually every lake for which we have fish tissues has come back with a mercury consumption advisory," he said.
In Douglas County, 26 lakes out of 26 tested have consumption advisories from the state Health Department. Many of those lakes, plus creeks and wetlands, are also considered impaired by the Minnesota Pollution Control Agency. Mercury isn't the only contaminant that lands a water body on the impaired waters list.
A consumption advisory will likely be issued this winter for Lake Aaron, said Pat McCann, fish advisory program manager for the Health Department. She said her department advises Minnesotans in general to limit consumption of bass, walleye and northern pike, especially the bigger, older fish. Since mercury is considered so toxic, women of childbearing age and children under age 15 should eat those fish once a month at most, while men and older women are not as sensitive and can eat them once a week without health effects.
Lake Aaron's smaller fish, such as sunfish, crappies, bullheads and yellow perch, are considered low in mercury and can be eaten once a week, according to state websites.
Mercury poisoning can cause loss of peripheral vision; tingling in the hands, feet, and around the mouth; lack of coordination; impairment of speech, hearing and walking; and muscle weakness, according to the U.S. Environmental Protection Agency.
Minnesota considers waterways to be impaired when enough fish test positive for mercury levels at above .2 parts per million, said Bruce A. Monson, a researcher with the Pollution Control Agency. If more than 10 percent of a tested fish species includes that level of mercury, the waterway is listed as impaired.
Researchers tested eight walleye, eight northern pike, and eight largemouth bass caught in Lake Aaron in 2016. Average mercury concentrations for the three species were 0.25, 0.44 , and 0.39 parts per million, respectively, Monson said.
Being added to the list of impaired waters means the state is required to develop a cleanup plan for Lake Aaron, which is particularly problematic because of the widespread nature of mercury contamination. The largest source of mercury contamination in the United States comes from coal-fired power plants, according to the EPA.
While a coal-burning plant operates as near to Douglas County as Fergus Falls, the MPCA estimates that 90 percent of mercury contamination comes from outside the state and even outside the country, said Cathy Rofshus, the agency's lead information officer for all water programs.
"That's the tough part with mercury," she said.
While Minnesota has work to do on reducing mercury emissions, it can also use the data on its impaired waters list to show other governments how their emissions affect us, she said.
It's also important to remind anglers to limit how much fish they consume, and pay attention to the lakes the fish come from, she said. Mercury tends to be more of a problem in northern Minnesota than in the southern part of the state, Rofshus said.
While addressing water pollution can seem hopeless, she pointed out that for the first time, the state has found that some waterways are recovering from PCB contamination.
"It takes a long time, but the water can get better," she said.