HERE'S A RARE GOOD WORD for the zebra mussel, scourge of the Great Lakes for the past 10 years. Yes, they clog the water-intake pipes of factories and power stations, costing $6 million yearly in cleanup fees for Lake Erie, which is infestation ground zero. And by competing with fish for plankton, zebra mussels have helped cut Lake Erie's sportfishing business--$600 million a year in 1984--by two-thirds.
But the mollusks are cleaning up murky lake waters. By ravenously filtering floating particles, they're bringing back long-vanished water plants, such as tape grass, says Ohio State University biologist Ronald Stuckey. Another factor: recent curbs on phosphate pollution.
Their water-clearing effects have hardly won the mussels a reprieve from eradication efforts. There's new bad news: Scientists now suspect they may eat toxic chemicals on lake bottoms, which are then absorbed by fish that feed on the mussels. While the theory has yet to be proved, the toxins may end up on dinner plates. Also, experts believe the mussels altered the Lake Erie ecosystem this summer and caused a huge bloom of toxic algae.