Dutch John — The parasite that causes whirling disease has been found in four rainbow trout taken from the Green River below Flaming Gorge dam.

Most of the trout in the upper Green River are brown trout. Brown trout are very resistant to whirling disease.

Photo by Matt McKell

Whirling disease doesn't harm people, but it can kill small trout, especially small rainbow trout.

Fortunately, Division of Wildlife Resources fish pathologists and biologists don't expect the parasite will affect fish populations in the Green River to any great degree:

• Most of the trout in the eight-mile stretch below the dam are brown trout. And brown trout are very resistant to whirling disease.
• Rainbow trout are more at risk if the rainbow trout are small.

The rainbow trout that the DWR stocks into the upper Green River average eight inches long when they're stocked, so the trout are too large for the parasite to affect them significantly.

"We don't expect trout in the upper Green River to be greatly affected," says Roger Wilson, chief of the DWR's Aquatic Section. "The upper Green River should remain one of the best trout fishing waters in the country."

Not a surprise

DWR fish pathologists and biologists weren't surprised to find the parasite that causes whirling disease in the four fish. The parasite was confirmed in 2010 in kokanee salmon the biologists collected as the salmon migrated from Flaming Gorge up Sheep Creek to spawn. And Wilson says the parasite has been in streams and rivers that empty into Flaming Gorge for years.

A sample of 20 rainbow trout collected in September 2010 confirmed their suspicions. The trout were collected about seven miles below the dam at Little Hole. After being collected and placed in a freezer, fish pathologists at the DWR's Fisheries Experiment Station tested the trout earlier this summer.

DWR Fish Pathologist Chris Wilson says while four of the trout had the parasite, none of the four fish contracted the disease. "To contract the disease," he says, "trout must be heavily infected with the parasite at a young and fragile age. The trout we release into the upper Green River don't fit that category. And the wild brown trout in the river are much more resistant to the disease."

How you can help

While whirling disease shouldn't affect trout in the upper Green River much, the disease can affect smaller trout in other bodies of water.

To avoid spreading the disease to other waters, DWR biologists encourage you to do the following (the following will also lessen the chance that you move New Zealand mud snails, quagga and zebra mussels or other aquatic invasive species from one body of water to another):

• Don't use wading boots that have a felt sole. Felt-soled wading boots can pick up whirling disease spores and move them from one body of water to another. It's difficult to completely clean and disinfect felt-soled wading boots.
• After you're done fishing, clean all of the mud off of your fishing equipment, including your boat, trailer, waders, boots, float tubes and fins. Thoroughly dry the equipment in the sun before using it in other waters.
• If you're traveling directly to another body of water, clean your equipment with a solution that's 10 percent chlorine bleach and 90 percent water. Or, better yet, use another set of equipment.
• Don't dispose of fish heads, skeletons or entrails in any body of water. Instead, place the fish parts in the garbage, bury them deeply or burn them completely.