Montana Fish, Wildlife & Parks has observed recent mortality of mountain whitefish in several sections of the Yellowstone River.

The cause of the mortality is still unconfirmed. However, these circumstances appear to be consistent with what has been observed in fish that die due to proliferative kidney disease, or PKD — a condition caused by a parasite affecting salmonids, such as mountain whitefish and trout. PKD has affected fish in the Yellowstone River in recent years, the most significant outbreak happening in 2016.

FWP has worked with other agencies to submit samples for testing to determine whether PKD is a factor in this most recent whitefish mortality.

FWP began receiving reports of dead whitefish last week. Since then, biologists have surveyed several sections of the Yellowstone River to gather more information.

• On Wednesday, biologists observed seven dead whitefish over about 9 miles from the Springdale Bridge Fishing Access Site to the Grey Bear Fishing Access Site, upstream from Big Timber.
• On Thursday, biologists counted 149 dead whitefish over almost 9 miles between the Pig Farm Fishing Access Site and the Springdale Bridge Fishing Access Site, downstream of Livingston.
• On Friday, they counted 38 dead whitefish over 20 miles between the Pine Creek Fishing Access Site and the Highway 89 Bridge Fishing Access Site, upstream from Livingston.

No trout mortality was observed during last week’s monitoring efforts.

FWP will continue to monitor conditions on the Yellowstone River. At this time, no closures or restrictions are expected for the Yellowstone River or its tributaries.

Anglers can help reduce stress for fish by following these practices when catching and releasing fish: ​

• Land the fish quickly.
• Wet your hands before handling the fish.
• Keep the fish in water as much as possible.
• Remove the hook gently. Using artificial lures with single and barbless hooks can make hook removal faster and easier. If the fish is hooked deeply, you may have to snip the line at the fish's mouth or consider keeping it if regulations allow.
• Let the fish recover before releasing it.