A Mystery of Fish Mortality

Elusive Illness Plagues Some Virginia Rivers

MORGAN FORD, Va. -- Something in the Shenandoah River is turning the smallmouth bass thin and listless and causing sunfish to break out in blisters that look like cigarette burns. Something in the water is making both species weaken and die, leaving the river bottom flecked with white bellies.

Something is doing all this. After five years of tests, more than $600,000 in government money and uncounted numbers of dead fish, that's still as much as anybody knows.

Since 2002, fish have been dying in the Shenandoah and other western tributaries of the Potomac River, and scientists have been racing to find the cause. They have considered viruses, oxygen-depleted "dead zones" and runoff from chicken farms, but they have found nothing definitive. At the same time, the search has been complicated by die-offs this year in two rivers outside the Potomac watershed: the Cowpasture and upper James.

At the center of the mystery is the Shenandoah, whose easy fishing and picturesque setting have long attracted visitors from the Washington area. Here, the impact has been ecological, economic and emotional, as locals try to understand how this beloved waterway became something that kills fish.

"It was such a beautiful river and everything," said Chuck Kraft, a longtime fishing guide from Charlottesville, who has stopped bringing clients to the Shenandoah. "It's kind of sad, you know. It's like losing a friend or a family member."

This spring and summer, dead fish have been reported in six waterways that begin in the mountains near the Virginia-West Virginia border. Four are part of the Potomac River watershed: the North Fork of the Shenandoah, the South Fork of the Shenandoah, the main body of the Shenandoah and the South Branch of the Potomac. The other two are part of the James River watershed.

Often, dead fish have large blisters on their sides or patches of fungus that look like cotton balls. Sometimes, the gills are so inflamed that they can no longer filter oxygen out of the water.

"You don't see a lot at one time, but you see some everywhere you look," said Bill Hayden, a spokesman for Virginia's Department of Environmental Quality.

The kills are not thought to signal a threat to human health. No risk is seen to people who swim in the affected rivers or Washington area residents whose drinking water is drawn from the Potomac downstream. But it troubles scientists that the same types of fish, with the same problems, have been dying in the region since 2002.

"We can't say it's the same thing," Hayden said. "But it is very similar."

A 2002 fish kill occurred in the South Branch of the Potomac in West Virginia. Beginning in 2004, die-offs followed in the Shenandoah and its two main tributaries, which wiggle through mountain valleys just beyond Washington's western suburbs.

In each case, scientists have looked for the usual suspects in any fish kill -- a toxic algae bloom, a malfunctioning sewage treatment plant, an overturned chemical truck -- and found none of them. Instead, some of the fish were being killed by bacteria that they would normally be able to fend off. Something, apparently, was weakening their immune defenses.