Thousands of dead fish are washing up on the shores of Lake Erie and the cause of the deaths is unknown. Fish carcasses lie rotting in coves and on beaches. The stench has gotten so bad that it?s forced homeowners to keep their windows closed.

?It?s a very interesting mystery,? says Bill Culligan, an aquatic biologist who heads the Lake Erie Fisheries Research Station. Scientists are looking into whether a virus, bacteria, weather-related events or zebra mussels may be to blame.

Several near-dead fish were collected and sent for analysis to labs at Cornell University and the state Department of Environmental Conservation, near Albany, New York. The heat caused most of the fish to decay too quickly to test. ?One problem we?ve had testing is you need very fresh fish to do cultures,? says Culligan. Lab results are expected in one to two weeks.

The die-off has occurred steadily through the summer in the eastern third of the lake, from Ontario, Canada, through New York and into Pennsylvania. The number of dead fish is estimated to be tens of thousands.

Jeff Connors runs along the shore every morning, about 15 miles southwest of Buffalo. While dead fish are a fairly common sight at the end of the summer, he says, ?there?s never this much, and never so early. You?ve got to watch where you?re stepping.?

The stench of dozens of decaying fish fills the air. ?It?s bad but it comes and goes,? says Jennie Smaldino, who runs a hot dog stand at the marina.

Culligan says scientists first attributed the deaths to weather-related events called upwellings, when strong winds blow the warmer surface water to the other end of the lake and deeper, colder water comes to the surface. A July 27 upwelling dropped the lake temperature 23 degrees in a matter of hours. ?But fish are also dying at other times,? he says, so scientists are searching for other explanations.

The round goby fish, a recent lake invader, is one suspect. ?Until the round goby showed up, nothing ate the zebra mussel,? says Culligan. The gobies are eaten by sheephead fish and the other bottom feeders. While they?ve been a blessing in helping to reduce the number of zebra mussels, they may be poisonous to other fish.

Lake residents have their own theories. Betty Maslow of Point Breeze wonders whether the lower lake level has played a role. ?Our beach is twice the size it was last year,? she says.

The fish die-off has led to the deaths of a smaller number of seagulls and other scavengers. The birds die from a type of botulism, a toxin which forms as the fish decay.

Environmentalists fear more birds, including migrating loons, will fall victim to botulism if the fish die-off continues into the colder weather. Last year, a different strain of botulism killed more than 8,000 water birds along Lake Erie in late fall.

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