Over the past few weeks, the Yellowstone River between Gardiner and Springdale (east of Livingston) has undergone a dramatic fish kill primarily involving mountain whitefish. The worst effects of this kill seem to be occurring in lower Paradise Valley, from somewhat below Emigrant down to Livingston, where upwards of 4,000 dead whitefish have been found and estimates of total mortality extend into the tens of thousands of whitefish. The effects have been far smaller near Gardiner. Our guides have seen perhaps fifty dead whitefish between Gardiner and Carbella Access some 17 miles downstream of Gardiner. No fish kills have been reported in Yellowstone National Park. Thus far, the fish kill is almost exclusively impacting whitefish, with confirmed reports of only three dead trout found by Fish Wildlife & Parks survey crews. It is unclear (to me) whether these fish died due to the same pathogen or whether they died from some other cause.
Lab studies show that the whitefish have fallen victim to a microscopic parasite called Proliferative Kidney Disease. This disease can cause extreme mortality in both whitefish and trout. In the most recent kill in our region, in Idaho’s South Fork of the Snake and Henry’s Fork of the Snake in 2011, trout impacts were minimal but whitefish impacts were extreme. The spread of this illness and its effects are exacerbated by low water, warm water, and angling and other stress factors. To protect the Yellowstone’s trout population and to prevent the spread of the parasite responsible for the disease, Montana Fish, Wildlife, and Parks has closed the entire Yellowstone River drainage from the Yellowstone Park boundary at Gardiner down to the city of Laurel, past the primary coldwater sections of the river. This closure includes all free-flowing tributaries (small streams, the Boulder, Stillwater, and Shields River systems, and the Paradise Valley spring creeks). It is unclear to me whether this closure includes private lakes separated from the main flow of the river drainage. The Bighorn River is east of the closure zone and is not impacted. The impacted waters are closed to ALL recreational activities, including fishing, boating, and swimming.
Yellowstone National Park waters as well as small streams that begin in Montana north of Yellowstone Park but flow into the Yellowstone River upstream of Gardiner are not impacted by the closure. Of particular note, Yellowstone National Park fisheries staff have found no fish kills within the park boundaries and as of August 20 have no plans to institute closures within the park. This might change, but it would surprise me if it does. Low, warm water is a contributing factor to the disease, and Yellowstone National Park waters are higher, colder, cleaner, and with some exceptions see less pressure than waters outside the park. The lack of any fish mortality within the park jives with what I have seen just north of the park. Guides fishing lower down the Yellowstone near Livingston have seen literally hundreds of dead whitefish in a day. I have not seen more than a half-dozen in a day. Here is the park news release on the subject. Check here for any additional news releases on the subject.
The Yellowstone River will not reopen until conditions improve and the whitefish stop dying. I believe this will happen sometime between the Labor Day holiday and the 20th of September. Cooling water temperatures and the lack of fishing pressure will make a difference. I suspect FWP will begin considering reopening the river just after Labor Day, to save the fish the pressure from the holiday. That said, if the whitefish quit dying, they might reopen the river in the next week. If trout start dying in large numbers, the river might not reopen this fall.
In the meantime, the key duty of all anglers who like fishing Montana and the Yellowstone Region is to clean, dry, and disinfect all watercraft and wading gear before traveling to another waterbody, if you’ve visited the Yellowstone River in the past few weeks. I have extra wading gear that I’ll be using in Yellowstone Park for the next couple weeks, until my gear I used in the Yellowstone itself is thoroughly dry and all risk of contamination is gone.