Wilfred LePage saw his first zebra mussel Feb. 1. By September, thousands of the tiny molluscs jammed the intake of the water treatment plant he manages, cutting the flow 20 percent and nearly sparking a water emergency. ``There is no cheap solution to it and there's no real cure to the problem,'' said LePage, water treatment superintendent in Monroe, Mich., on Lake Erie's western edge. At the eastern end of the lake, in Dunkirk, N.Y., the green-and-yellow striped shellfish first appeared Oct. 3, and now infest a Niagara Mohawk Power Corp. generating plant. December's deep freeze stopped them from clogging water intakes but they quickly settled inside the plant. ``They like it where it's dimly lit, they like it where it's warm, and they don't like a lot of turbulence. This place is ideal for them,'' said Robert C. Henderson, a chemical lab supervisor at the plant. ``By July, we're going to have a massive problem with them.'' Three years after they were introduced to North America and after only one year in Lake Erie, zebra mussels have spread throughout the lake and have been spotted at the entrance to Lake Ontario and along the St. Lawrence River. It's an invasion scientists say could affect farming, fishing and daily life along virtually every body of fresh water in North America in the next few years. The mussels are mostly about a half-inch long, although they can reach 2 inches during their five-year lifespans. They eat by filtering microscopic food particles from the water, and love intake pipes of water and power plants because the current brings them a steady supply of fresh food. A mussel can filter more than a gallon of water an hour, said R. Warren Flint, a scientist with the Great Lakes Program at the State University of New York-Buffalo. As a result, they will leave water cleaner than before. ``From an aesthetic perspective, that would certainly be a benefit, I guess,'' he said. Europeans have used zebra mussels to clean algae-choked ponds, and the shells can be used to add calcium to livestock feed, said Charles O'Neill, with the Sea Grant program at the State University College at Brockport. The mussels also are a good source of food for diving ducks and some kinds of fish, including sturgeons and eels, Flint said. But with millions of them at work filtering microscopic food, they could deplete the supply for the small fish that support the billion-dollar walleye- and bass-fishing industry. And the bad news could spread beyond the lake and its shoreline. Farmers and golf courses that draw irrigation water from the lakes can expect problems, and beachgoers will have to wear shoes because of the shells, O'Neill said. ``It can affect everything from the electricity at your outlet to the water at your tap,'' O'Neill said. ``It's not just an environmental problem.'' Like their distant cousins, the blue mussels, zebras ought, in theory, to be edible by humans, Flint said. But when Canadian researchers tried steaming a bunch, O'Neill said, ``What they got was a stench that cleared the lab.'' The mussels have plagued Europe for more than a century and are believed to have arrived in North America on a freighter that emptied its ballast tanks in Lake St. Clair, upstream from Lake Erie, in 1986. Scientists are studying the possibility that the Lake Erie infestations came from several ships rather than that single 1986 event, O'Neill said. But Flint said one colony could have infested the lake because one mussel can lay 30,000 to 50,000 eggs a year and the larvae can swim for up to two weeks before growing shells. ``They could easily get across Lake Erie or Lake Ontario in that period of time,'' he said. For public water systems, controlling the mussels is a matter of applying chlorine, ozone or other disinfectants at the mouth of the intake pipe rather than waiting until the water is inside the plant, say scientists and plant operators like LePage who have already faced the problem. Power plants have a different problem, because officials are reluctant to let them put chlorine or other disinfectants in cooling water discharged back to the lake, Henderson said. Niagara Mohawk and the state Department of Environmental Conservation are negotiating a solution. James Sell, chief operator of the Dunkirk water plant, is studying ways of getting chlorine to the pipe's mouth, like building a platform over the intake or running a smaller chlorine pipe out through the intake. ``We're better off than the people in the western end of the lake,'' Sell said. ``At least we have some time to do something by spring.'' The City Council hasn't been persuaded to pay up to $100,000 for the plans, but Sell, who keeps three living mussels in a jar to show visitors, said, ``I don't see much option for them if they want a water supply.'' Farther inland, many water officials are unaware of the problem or not prepared to do anything about it. Michael Burke, director of the state Health Department's bureau of public water supply protection, said the department was studying the problem but doesn't see the need to issue warnings. ``I think the word's getting to them, particularly those with large surface intakes in the Great Lakes. It is coming out in industry papers and things of that sort.'' O'Neill and other scientists said the state should do more to get the word out, because it is only a matter of time _ and not necessarily very much time. ``The chances of them getting into the western reach of the Erie Canal is good,'' O'Neill said. ``The canal is an ideal place for them to live. It's warm. It's shallow. Most of it has rock riprap to attach to.'' Pleasure boats can also carry mussels and their larvae in their engine housings and other places where water collects. Once the mussels get into Lake Michigan, they will almost certainly spread through the Chicago River and into the Mississippi River basin, O'Neill said. ``Any area in North America that is utilizing surface water should be concerned.''