FREMONT - You wouldn't know it by looking at all the mayflies in Toledo, Monroe, and Port Clinton this week, but the tiny winged insect - a symbol of Lake Erie's ecological comeback - apparently has experienced a setback in recovery efforts between Sandusky and the Pennsylvania state line.

No mayfly nymphs were found this spring in 30 shoreline sampling locations from Sandusky to Conneaut, Ohio.

The central and eastern parts of the Lake Erie shore typically have sparse mayfly production because of deeper water and colder temperatures, although the bug had started to show promise for establishing itself there.

Last year half the sites tested on the far eastern side of Ohio's Lake Erie shoreline had mayfly nymphs. In 1999, 44 percent of those in the central area had them, Dr. Ken Krieger, the state's best-known mayfly researcher, yesterday told the Ohio Lake Erie Commission at Terra Community College in Fremont.

“I would not post a red flag yet. I would post a yellow one, though, because it appears something has changed in the central [and eastern] basin since [May, 2000],” said Dr. Krieger, senior research scientist at Heidelberg College's water quality laboratory in Tiffin.

The commission is a coalition of state agency directors that oversees much of the state-funded research on the lake. It meets four times a year.

Mayfly nymphs are akin to baby bugs. They burrow in sediment for two years before reaching adulthood and sprouting wings. Researchers count the nymphs to estimate future swarms.

Besides being an ecological symbol, mayflies are an important source of food for walleye and yellow perch, two of Ohio's most coveted sport fish.

By far the greatest mayfly production is on the western end of the lake, because water is much shallower, and therefore warmer, because sunlight has an easier time penetrating it. That's why Toledo, Monroe, and Port Clinton usually get the brunt of the swarms, although a lot depends on wind.

This year's swarm is expected to reach its peak for those communities this week, Dr. Krieger said. “It looks like a healthy population, but I'm not sure how strong their hold is on the region,” he said.

The lack of nymphs in sediment east of Sandusky could be a one-year fluke - or a sign of something worse, Dr. Krieger said. Mayflies are sensitive to pollution and had all but disappeared from the lake until the early 1990s.

First Published June 21, 2001, 11:41 a.m.