Virginia environmental officials are passing the hat to help pay for ridding a Prince William quarry of aggressive zebra mussels. They say the effort would be the one of the largest ever attempted.

Once established in rivers and lakes, the mussels multiply rapidly. Although they don't harm water quality, the mollusks kill off marine life, clog drinking water intakes and cost millions of dollars to control. The quarry, near Haymarket, is only 300 feet from Broad Run, a tributary of Lake Manassas and the Occoquan Reservoir, which together provide drinking water for 600,000 people.

The dime-size mussels, originally from the waters of Russia and Ukraine, live in fresh water and probably couldn't survive in the saltier parts of the Chesapeake Bay, but they could still pose a danger where the bay's waters are less brackish, experts say.

State officials have $400,000 in federal money for the eradication project, which they estimate is half of what it will cost to rid the 12-acre, 100-foot-deep quarry of the mussels. State officials have asked local water and other officials to provide the balance.

Thus far, only the Fairfax County Water Authority has responded by pledging $200,000 for the effort and offering to put up the rest so the state could quickly put the project out to bid, said Jeanne Bailey, a spokeswoman for the agency. The authority would hope to recoup most or all of the additional $200,000 it plans to provide, she added.

According to W. Tayloe Murphy Jr., Virginia's secretary of natural resources, soliciting local governments, water suppliers and private organizations for the needed money is unusual.

"We have a problem and there is no money in the budget,'' he said. "I am pleased with Fairfax Water's response. . . . The general response has not been overwhelming.''

The challenge for biologists is "to select a method that would both eradicate the mussels and not hurt the surrounding groundwater, surface water or other fish or wildlife," said Ray Fernald, manager of environmental programs for the Virginia Department of Game and Inland Fisheries.

The danger is that the mussels could be washed from the quarry into Broad Run during heavy rains. So far, that has not happened.

"We're always worried," Bailey said. "It's been a very wet couple of years, and we've been very fortunate."

Water officials don't want to continue pushing their luck. The zebra mussels have spread throughout the Great Lakes since they were first spotted in the mid-1980s. Juvenile mussels are the size of a grain of sand and can be easily transported on the propeller of a boat, on the feet of a duck or in the equipment used by scuba divers. It costs more than $5 billion a year to control them.

The mussels in Prince William were discovered in fall 2002 by a diver who recognized the species and the problem.

Environmental officials suspect that recreational divers may have imported the mussels by accident or purposefully. One of the byproducts of the mussels is that they clear up the water, an advantage to divers. An investigation into the matter by state officials is still pending.

Fernald said there are many ways to kill zebra mussels, but deciding on the best method will be the challenge. The method chosen will help determine the time frame as well.

"You can freeze them, dry them, shock them or drive all of the oxygen out,'' Fernald said. There are also chemicals, such as chlorine, copper sulfate and potassium, that that can be dumped into the quarry and will do the trick.

Zebra mussels have been successfully eradicated from isolated areas such as in ballast water, near chemical plants, dams and other sites, he said.

"No one has ever tried to eradicate such a population in open water,'' Fernald said. "And we want to be as environmentally benign as possible.''