WY Game and Fish Identifies Disease as Cause of Salt River Fish Die-Off

The Wyoming Game and Fish Department has identified Proliferative Kidney Disease as the cause of a fish die-off that may have killed thousands of mountain whitefish in the Salt River.

Specialized testing conducted by the department’s Fish Health Laboratory, with assistance from the Wyoming State Veterinary Laboratory, confirmed the presence of Tetracapsuloides bryosalmonae, the microscopic parasite responsible for the disease, commonly known as PKD. Investigators also found evidence that the parasite caused the observed deaths.

“This event marks the first documented instance of a PKD outbreak causing significant fish mortality within Wyoming,” Jackson Region Fisheries Supervisor Darren Rhea said. “While it is difficult to get an exact count, we suspect that total mortality may number in the thousands.”

Mountain whitefish appear to be the species most affected by the outbreak. PKD has previously caused fish deaths in neighboring states, including Idaho and Montana. A major 2016 outbreak on Montana’s Yellowstone River resulted in a large fish kill and temporary river closures.

According to Game and Fish, PKD outbreaks are often connected to stressful environmental conditions, including prolonged low streamflows and elevated water temperatures.

“The parasite lives in tiny, moss-like organisms called bryozoans that form colonies in the water,” Fish Health Program Manager Carl Smith said. “These organisms then pass the parasite along to the fish.”

Researchers throughout the region are studying the relationships among the parasite, bryozoans, fish and environmental conditions that can cause severe outbreaks. Wyoming fisheries managers have long-term monitoring data for the Salt River and plan to conduct follow-up surveys in 2027 to measure the outbreak’s effects on the river’s whitefish population.

The Salt River remains open to fishing and other recreation. However, Game and Fish could impose emergency closures if mortality continues at a level that threatens the river’s long-term health.

Officials are encouraging anglers to consider fishing elsewhere during the outbreak to reduce additional stress on surviving fish.

Game and Fish also reminded recreationists to drain, clean and dry boats, waders and other equipment between trips. Live fish should never be moved from one body of water to another.

More information about preventing the spread of aquatic diseases and invasive species is available through the Wyoming Game and Fish Department.

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