CHICAGO — FIVE years ago a European freighter discharged ballast water containing zebra mussels near Lake Erie. Today's colony is so large that, as it feeds on phytoplankton, it can filter all of the lake's 116 cubic miles of water in one week. ``It sounds like science fiction,'' admits Susan Fisher, a marine toxicologist at Ohio State University.
Massive encrustations of zebra mussels can choke industrial cooling systems and municipal water plants. According to a United States government estimate, dealing with the striped mollusk will cost $500 million a year this decade.
The creatures are expected to spread into all the bodies of cold fresh water in North America, possibly on duck's feet or in boat engines.
They can survive two weeks out of water and ``tend to attach to places ... where you're not going to look too carefully when you get your boat home at 10 o'clock Sunday night,'' Dr. Fisher says.
In Europe, which has dealt with zebra mussels for hundred of years, 60 to 90 percent of the population have been reported to die every three to five years.
However, ``part of our problem is that we are basing all of our predictions on the European experience,'' Fisher says. Increasing dissimilarities give scientists here an ``uneasy feeling'' that the European data may not apply over here.
Some people have looked for a silver lining, noting that the mussels increase lake water clarity. But they do so by eating food that fish need. While clear water looks nicer, Fisher says, ``ecologically, it could signify a disaster.''
For all its intimidating traits, the zebra mussel is not ``an invader from outer space,'' Fisher reassures. It can be killed easily. The trick is to do so cheaply, and without harming other creatures or the environment. Hot water, ozone, chlorine, and commercial molluskicides are effective but have some of these drawbacks.
Last June Fisher set up the Zebra Mussel Testing Center to evaluate products proposed for use against them, and to design and produce compounds that affect only that organism. So far her lab has turned up a derivative of potassium phosphate that looks promising.
But Fisher believes that ``the bottom line is, we're going to have to learn to live with them.''