Hundreds of Dead Fish Discovered in Yellowstone River

An investigation has been launched after hundreds of dead fish were found in the Yellowstone River. Montana Fish, Wildlife & Parks (FWP) said the cause of death of around 200 fish is yet to be confirmed, but is believed to be the result of a proliferative kidney disease, or PKD, which is caused by a parasite in the water.

Reports of dead fish began at the end of August and since then biologists have been visiting different sections of the river to assess the situation. They found dead mountain whitefish across several sections of the river, which stretches almost 700 miles through Wyoming, Montana and North Dakota.

Biologists found 149 dead whitefish over a nine-mile area downstream of Livingston. Seven dead whitefish were found upstream from Big Timber, also over a nine mile stretch. A further 38 were found over 20 miles between the Pine Creek Fishing Access Site and the Highway 89 Bridge Fishing Access Site, upstream from Livingston.

The FWP is now working with other agencies to submit samples for testing. This will allow them to establish if PKD is the cause of death.

This disease is also known to affect trout, although the FWP found no evidence of this species being impacted by the potential outbreak in Yellowstone River.

The agency plans to monitor conditions on the river but says no closures or restrictions are currently in place.

PKD outbreaks in the Yellowstone River have been reported several times in recent years. The disease is characterized by severe inflammation of the kidney and anemia. Signs normally only develop after the water temperature goes above 15 degrees Celsius for a prolonged period, the National Park Service says.

In 2016, there was a major outbreak of PKD in the river, with thousands of mountain whitefish dying from the disease. Deaths were recorded between Emigrant and Springdale, Montana, and resulted in the closure of over 180 miles of the river.

The parasite that causes the virus, Tetracapusloides bryosalmonae, was not known to be endemic to Yellowstone River. This caused concerns it had been introduced and that it could spread upstream to Yellowstone National Park. Research that followed the 2016 outbreak showed T. bryosalmonae was widely distributed.

"Many regional rivers had hydrologically stressful conditions similar or worse than the Yellowstone River in 2016, yet there were no documented PKD fish kills," a report by the National Park Service said. "These results...suggest that warm temperatures and low flow conditions cannot alone explain PKD-caused fish kills. This unanticipated die-off further underscores our limited understanding of PKD."

mountain whitefish
Dead mountain whitefish in the Yellowstone River during the 2016 outbreak of PKD, where thousands of fish died. Park officials are now investigating the deaths of around 200 fish. William Campbell-Corbis/Getty Images