Mayfly abundance offers signs of healthy Lake Erie

Port Clinton, Ohio — Swarms of mayflies are beginning to show up along Lake Erie, and that is a good sign, say experts who study the lake’s ecosystem and overall health.

“It’s in full swing,” said Christopher J. Winslow, assistant director of the Ohio Sea Grant Program who also helps coordinate research at Ohio State University’s Stone Lab near Put-in-Bay on Lake Erie. “I was there last week (June 9). We had piles of mayflies under the lights. They are out in good numbers.”

Winslow expects the peak of swarming to hit by the end of June as millions of these harmless but pesky insects ascend from the mud or sediment of the lake and swoop into surrounding coastal areas, attracted mainly by lights.

Mayflies only live about a day or two. They will cling to windows, street lights, and various other places in the towns that dot the Lake Erie coastline. Since they have no mouths, they have no way of feeding.

“If you see a lot of mayflies, you definitely have a healthy ecosystem,” Winslow said.

And that means the overall health of the lake is good, too. Fish and seagulls are among lake-dwelling creatures that eat mayflies as a source of protein.

Back in the 1960s and 1970s when industrial toxic pollutants and dumped wastewater were prevalent in Lake Erie, these insects almost died out. They have recovered in recent decades.

“Over the years, a lot of the industrial pollution (and wastewater) has been cleaned up,” said Dina Pierce of the Ohio Environmental Protection Agency. “We’ve been doing studies on streams that feed into Lake Erie. We haven’t directly studied (toxic pollution) impact on mayflies.”

After mayfly larvae hatch from eggs that sink into the lake, the larvae burrow into the sediment of the lake. It can take up to two or three years for the mayflies to mature. During that time, any toxic pollution in the lake could have an adverse impact on the mayfly population.

However, Winslow pointed out that a short-term drop in the mayfly population could also be the result of a poor mating season two or three years earlier.

Females drop fertilized eggs into the lake during a roughly three-week period in the summer. If the weather is stormy and windy during that time, it could affect what happens to the eggs and larvae.

A recent concern has been the increased frequency of toxic algal blooms in the lake. These blooms are thought to be creating “dead zones” in the central basin of the lake where oxygen is sucked away.

Gail Hesse, executive director of the Ohio Lake Erie Commission in Sandusky, recently chaired the Ohio Lake Erie Phosphorous Task Force, which took a look at algal blooms, among other things. A report on the task force’s findings is due out in several weeks, she said in mid-June.

Mayflies are a sign of reasonably good water quality, Hesse said, but added that there is not a lot of research yet on the impact of algal blooms on the lake’s ecosystem.

A lot of the phosphorous contamination appears to result from fertilizer runoff from farmland into the streams and rivers that feed Lake Erie. The end of June is usually when a forecast is made on what impact that runoff is having on the lake.

“The algae is an ever-changing situation,” she said. “It’s variable from year-to-year and moves by winds and waves. It doesn’t stay in any one location.

“Decomposition (of the algal bloom) eats up the oxygen . . . and contributes to the dead zones,” Hesse said.

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