Eight years ago, when Paul Pacholski heard that toxins from an algal bloom in Lake Erie had contaminated Toledo’s drinking water supply, he worried how that would affect the sport fishing industry. “We wanted to find out immediately what the effects of [the toxins] were on the fish that we were consuming and encouraging people to eat,” said Pacholski, who had spent decades as the captain of the Erie Hopper, guiding tourists to his favorite spots for walleye and perch. So when subsequent studies showed the fish did not retain high levels of toxins in their fillets, he says, “that put a lot of people’s minds at ease.”
A new study published in the journal Science of the Total Environment, however, shows that while Lake Erie fish fillets are safe to eat, the fish themselves may not be doing so well. In a first-of-its-kind study, researchers over multiple years gathered samples of walleye, yellow perch, white bass, and white perch before, during, and after harmful algal blooms appeared in the lake’s western, west-central and east-central basins. They then measured the amount of microcystins — a class of toxins produced during some algal blooms — in the animals’ livers.
During blooms, the scientists found microcystins at levels of up to 7,177 micrograms per liter, which is 7,000 times higher than the World Health Organization (WHO) limit for human ingestion. Most people don’t eat fish livers, of course, but the authors wanted to highlight that humans avoid drinking or swimming in water when microcystins reach a much lower level. But what surprised them the most was that some fish still had high levels — up to 547 micrograms per liter — even before a bloom, which suggests they were retaining some level of toxins in their livers throughout the year. The fish are exposed to the toxins from ingesting water, breathing oxygen through their gills, and eating smaller organisms that have also been exposed.
As a graduate student at Ontario’s University of Guelph, René Sahba Shahmohamadloo, first author on the study, conducted lab research using trout as a proxy for walleye and yellow perch, which are difficult to raise in captivity. He found that “even brief microcystin exposure of four to seven days can trigger stress responses in fish, and that’s at lower levels of exposure than what the wild fish are encountering.” In his research, the fish developed lesions on their livers and experienced hemorrhaging of the livers’ blood vessels. He also found proteins related to oxidative stress and cancer formation. The WHO considers microcystins potentially carcinogenic to humans and animals.
The latest results, Shahmohamadloo said, show that what happens to fish in the wild is worse than what he found in the lab. “We face a crossroads given these results,” he said. “Just because it’s safe for us to eat them, does this mean toxic algae blooms should continue, unabated, and threaten their existence?”
Richard Zweifel, fisheries manager for the Ohio Department of Natural Resources, said he was dubious that microcystins are lethally harming fish populations in Lake Erie. “I’ve never heard of a fish kill in Ohio resulting from exposure to high levels of microcystin toxins,” he said in an email. “Low dissolved oxygen resulting from excessive nutrient inputs (like a manure spill) are the most common cause of fish kills.”
Amy Holtshouse, director of conservation for the Nature Conservancy in Ohio, said she found the study intriguing. “I think it’s an absolutely valid and interesting question to be looking into what it means for the food web and the food chain,” she said. “It doubles down on the idea that we really need to address what’s driving this problem.” Lake Erie contains just 2 percent of the water in the Great Lakes but 50 percent of the fish.
Holtshouse said the algal blooms in Lake Erie are primarily the result of fertilizer — which contains phosphorus and nitrogen — running off farm fields in the Maumee River Basin, then flowing into the western part of the lake. She said there are a range of strategies farmers can use to address the problem, such as applying fertilizer more carefully and planting cover crops to hold those nutrients in place.
In 2018, the U.S. and Canada signed an agreement to reduce the amount of phosphorus entering Lake Erie by 40 percent from 2008 levels. There is no time line for either country to achieve those goals. Except for a few minor new regulations — such as not applying fertilizer on frozen ground or within 24 hours of predicted heavy rainfall — the approach is more carrot than stick, Holtshouse said. “There’s not an appetite for new regulations.”
Zweifel said his agency conducts tests on Lake Erie fish fillets — though not livers — before, during, and after algal blooms. That narrow scope concerns Shahmohamadloo, who said government agencies and the media tend to focus the majority of their attention on how algal blooms and microcystins affect humans but pay little attention to the fish. “These are species that are integral to the biodiversity of the lake and the food web,” he said, adding that as climate change worsens — raising water temperatures and increasing the frequency and severity of storms that sluice nutrients into waterways — so will the duration of harmful algal blooms that expose fish to microcystins. This year’s Lake Erie bloom lasted into November.
Pacholski said charter boat captains found a good number of walleye last year but that in the previous six or seven years, walleye fishing “was a total waste of time.” As head of the Lake Erie Charter Boat Association, he and his members help collect water samples and monitor algae and toxin levels for scientists at Ohio Sea Grant, a state, federal, and academic partnership housed at Ohio State. “We don’t do it for the business part,” he said. “We do it for the ecology, because we believe if you take care of the lake, it takes care of you.”