An invasive parasite that devastated fish population in some Western streams is showing up in Tennessee rivers, posing a health risk to fish and an economic threat to fishing guides and the multi-million dollar sportfishing industry.

Whirling disease is a condition caused by parasite that affects only trout and salmon species. Infected fish may developed a deformed skull and tail and cause the fish to swim in an erratic, tail-chasing manor.

Fish with Whirling Disease

In March, the Tenenssee Wildlife Resources Agency surveyed trout populations in the South Holston and Watauga tailwaters. Some of the fish showed signs of the disease. The agency sent the fish to a lab for testing and announced this weekend that both brown and rainbow trout from both rivers tested positive for the disease.

"It could be very serious, but we're not 100 percent sure. It really depends on the system," TWRA Streams and Rivers Biologist Sally Petre said.

The parasite has ravaged rivers in Colorado and Montana, but Petre said different rivers respond to the parasite differently.

The parasite develops in a specific type of worm before it infects trout. That worm lives in sediment, or mud on the river bottom. Petre said different rivers are impacted by the parasite to different degrees based largely on the composition of the stream or river bed.

"Out west in Colorado and Montana, some of them had 90 percent mortality rate, but other places like Virginia, they've had whirling disease for a long time and they don't see those drastic population effects," Petre said.

According to Petre, the disease has not had a noticeable negative affected trout population, and preventing it from spreading to other waters is paramount.

"We are very worried about it spreading up into our wild trout streams," he said.

Though the disease has been found in both rainbow and brown trout, Petre said brown trout can live with the parasite and not show signs of infection, whereas the parasite commonly kills rainbows.

The parasite has not spread to a stream with brook trout, but Petre said brook trout are highly susceptible to the disease.

Brown trout are a large draw on the South Holston River, while the Watauga River is known for its density of rainbow trout.

"The abundance of fish that we have and the quality of fish that are in these waters is very hard to beat," said Troy Runyan, head guide at South Holston River Company.

Runyan and dozens of other guides have built a career because of the South Holston and Wautaga rivers' reputation as a top trout fishery, but whirling disease poses a threat to the rivers' productivity.

"When you have such a passion for a sport like fly fishing and you have an affection for fish, and to see it suffer or succumb to something like this, it's a tragedy for us," Runyan said.

Petre said the most essential step to preventing whirling disease from spreading to other rivers and streams is cleaning gear. Runyan said taking those steps is part of being a responsible sportsman.

"We're blessed to have these resources here for us," Runyan said. "For us to minimize the effects of whirling disease here, I think we as fishermen are stewards of the water, and we owe it to the future generations."

Petre said boarts, kayaks, paddles and wading gear should be cleaned and allowed to dry before entering another body of water.

TWRA said a wading boots and waders should soak in a solution of 10 percent bleach for 10 minutes.

The agency has set up a page of its website with more information on the disease and asks that anyone who encounters a fish that appears to be infected contact an agent by emailing twra.whirling.disease@tn.gov.