The best guess is that the die-off can be blamed on natural causes stemming from the stress of spawning and the cold, stormy spring, said Roger Knight, Lake Erie fisheries program manager for the Ohio Department of Natural Resources.
"It all kind of fits that picture," he said.
The worst is likely over, said Knight, who flew over the lake earlier this week and didn't see a huge number of dead fish. "It probably started a while ago," he said.
It's difficult to know how many walleye have died, but Knight estimated it was in the thousands based on phone calls coming into his office. Most have been around the Lake Erie islands and between Toledo and Port Clinton.
Whatever is killing them isn't a danger to people who catch and eat walleye out of the lake, Knight added.
The walleye may be one of the most important resources for towns along Lake Erie's western shore.
Fishing brings in close to $500 million in spending on equipment, food, fuel and hotels, according to the American Sportfishing Association. This weekend, about 250 professionals and amateurs are participating in a tournament in Port Clinton.
Towns celebrate the tasty fish in a variety of ways. In Port Clinton, they lower a fiberglass walleye from a crane every New Year's Eve, and Toledo's minor league hockey team is called the Walleye.
That's why any sign of trouble for the walleye is taken seriously along Lake Erie.
"When you see six or eight fish in a certain area, that's not right," Pete Harsh, a pro angler from Minnesota, told The News-Herald of Port Clinton.
Charter captain Dave O'Neal told the newspaper his customers were concerned.
Knight doubts the die-off will have any lingering effect on the lake's walleye population.
There are about 20 million walleye in Lake Erie, and up to 30 percent can die in year, he said.
Most of the dead walleye have a lot of fungus, another sign that is typical after spawning, Knight said. Walleye expend a lot of energy during spawning, and that leaves them vulnerable to disease and death, he said.
Researchers also are testing the fish for viruses to determine if that could be the cause, he said.