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:

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."

News Source: Utah DWR - Sep. 09, 2011