Salt River whitefish killed by parasite

JACKSON (WNE) — The Wyoming Game and Fish Department has identified a parasite as the culprit behind an ongoing die-off of thousands of mountain whitefish on the Salt River.

The department’s Fish Health Lab and the Wyoming State Veterinary Laboratory identified Tetracapsuloides bryosalmonae in samples of dead fish. The parasite causes a kidney disease in salmonid fish such as trout and whitefish.

Whitefish are more susceptible, and no trout were found dead on the Salt River, said Darren Rhea, Game and Fish’s fisheries supervisor for the Jackson Region. The number of whitefish dying has started to drop off, he said.

Anglers first reported sightings of dead whitefish in the second-to-last week of August. Fisheries managers suspected the parasite at that time.

The die-off marks the first documented outbreak of the parasite in Wyoming. That’s significant and came as a surprise, Rhea said. Previously, there have been outbreaks in Idaho and Montana, including on the Yellowstone River. Effects of the parasite are exacerbated by low flows and warm water, which make fish less able to clear infections.

There are no management actions fisheries managers can take to directly prevent another die-off, Rhea said. Indirectly, managers can improve habitat and conditions in the watershed to the best of their abilities. They also can continue to spread awareness about best practices to clean watercraft and prevent the spread of aquatic invasive species and diseases.

Managers could also use short-term remedies, such as closures, if there are significant numbers of trout dying, or could change the daily fishing limit, Rhea said.

This story was published on Sept. 4, 2026. 

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