A mysterious affliction is killing fish once again in the Shenandoah River region.

Anglers and state scientists are reporting hundreds of dead and sick fish in the Shenandoah River and its north and south forks. The fish apparently began dying last weekend.

"We're seeing dead and dying fish on numerous locations on those rivers," said Bill Hayden, a spokesman for the state Department of Environmental Quality.

The DEQ yesterday asked the public to report fish deaths so scientists can document the affected area and collect specimens to study.

"We want to get on top of this as quickly as we can," Hayden said.

The deaths have become a grim spring ritual since they began in 2003. No one knows what's killing the fish.

A task force, including state and federal agencies, universities and community groups, is investigating.

The task force was established in July 2005 after most adult smallmouth bass and redbreast sunfish died in the Shenandoah and its south fork.

Those two species have suffered the most.

In October, Gov. Timothy M. Kaine made up to $150,000 available to step up the investigation.

The fish deaths have hurt the tourism and recreation industries in the Shenandoah Valley, state officials say.

The north and south forks of the Shenandoah flow generally north through the Valley, joining at Front Royal to form the Shenandoah about 120 miles northwest of Richmond.

From there, the Shenandoah runs north to Harpers Ferry, W.Va., where it joins the Potomac River.

The dead and dying fish are typically afflicted with sores.

Something apparently is reducing the resistance of the fish to illness, but no one knows why that is happening, Hayden said.

Scientists will check some of the recently killed fish for parasites, viruses and other problems.