Musseling in.

In a rare show of mussel power, scuba-diving scientists on the Allegheny River are moving thousands of endangered bivalves to make way for bridge reconstruction in Forest County, Pennsylvania. But increased housing construction on the shores of the "wild and scenic" waterway is causing environmentalists new concerns.

At least 22 species of mussels are known to exist from the Kinzua Dam to Tionesta--a free-flowing, 80-mile stretch that U.S. Geological Survey specialists have been studying for five years. Last August, they determined that the river near West Hickory and Hunter Run, where two bridge projects are slated, now harbors the nation's largest population of Northern riffleshell and clubshell mussels--endangered since 1993. The previous record holder had been in an Indiana river.

"It's crazy huge," said USGS diver-ecologist Glenn Nelson. "It shows how really healthy the river is." Mussels feed by straining nutrients from water--filtering up to one liter an hour. Nelson and his team spent this past summer at West Hickory, scooping mussels--endangered and otherwise--from the substrate, documenting their size, type and location while underwater, and then handing them to volunteers who tagged and placed them into laundry tubs. They were moved upstream and put into suitable new substrate, one by one. "You can't crowd them," says Nelson. "Mussels don't like to compete for food."

Alison McKechie was one of the volunteers who spent long days tagging the mussels for follow-up survival studies, a process that involved dabbing each with Crazy Glue and affixing a tiny plastic ID. "We had a lot of stuck-together fingers," says McKechie, a water quality expert with the nonprofit Pennsylvania Environmental Council. "We had to be careful not to glue the mussels closed."

McKechie's greater concern, though, is the building boom on the shores of the river. Though nearby state gamelands and the Allegheny National Forest have enabled the mussels to proliferate, new homes are springing up where there once was wilderness, raising fears about bank erosion and water pollution that could impact the bivalves' habitat. "I'm trying to educate homeowners about leaving buffer zones at the water's edge and planting native trees and shrubs," she says. "When you ask them to leave 10 feet unmowed, they kind of freak out." CONTACT: Pennsylvania Environmental Council, [phone], www.pec pa.org.