In early August boaters and anglers on the upper Yellowstone River, a recreation and angling magnet in southwestern Montana, started noticing dead fish floating in the river. At first just a few, but within days, hundreds, then thousands of fish belly up in the current or lining the banks. Mostly they were mountain whitefish, with a few species of trout, dace and suckers mixed in. Fish kill estimates rose to tens of thousands within a week.

After a survey of the river, begun on August 12, Montana Department of Fish, Wildlife and Parks (FWP) took the extreme measure of completely closing 183 miles of river, from the Yellowstone Park boundary in Gardiner, Montana, downstream to Laurel, along with tributary streams like the Boulder and Shields rivers.

As Governor Steve Bullock announced, "A threat to Montana's fish populations is a threat to Montana's entire outdoor economy and the tens of thousands of jobs it sustains." Add to angling the economic impact of commercial rafting, whitewater boating, camping and the many businesses those activities support, from coffee huts and hotels to convenience stores.

As days passed, and dead fish keep accumulating, FWP scrambled to analyze tissue samples and come up with answers. What they found is more evidence of the ripple effects of a warming climate. Montana has had a hot and dry summer, enough so that the flow levels of major rivers have dropped to near historic lows, and water temperatures have warmed to as high as 70 degrees in the Yellowstone. Fish stressed by low flows and high temperatures became vulnerable to a parasite (Tetracapuloides bryosalmonae) that causes Proliferative Kidney Disease (PKD), leading to kidney failure and death.

Meantime, angling shops emptied out, raft trips were canceled, hotel rooms and cabins lost reservations, vacationers went elsewhere, or never came at all. River volume on the Yellowstone hovers within 250 cfs of its all-time low, and while temperatures fluctuate, they have consistently been 15-20 degrees higher than what is considered healthy fish habitat.

According to the FWP spokespeople, the magnitude of the fish kill is unlike anything their fish specialists have ever seen. The river closure, while extreme, is an attempt to remove any additional stress from the waterway, and limit the potential spread of the parasite on boat hulls, waders, or vehicles.

"It's been kind of desolate around here," reports Adam Wagner, owner of Sweetcast Angler in Big Timber.

After several public meetings, Governor Bullock declared an "invasive species emergency", thereby freeing up $15.4 for unemployment insurance and job retraining. For many, the help is too little and too late.

"We'll just have to make the best of it, I suppose," says Jimmy Kahl, co-owner of River Source Rafting Company in Gardiner, bemoaning the weeks of canceled trips he can't get back.

On a bigger scale, the Yellowstone fish kill provides another bitter dose of the unexpected side effects of a warming climate.

"It's just another indication of how these systems are changing," says Clint Muhlfeld, aquatic researcher at the Flathead Lake Biological Station in northern Montana.

A photo posted by Jen Wolpoff (@jenwolpoff) on

Over the past 20 years, unprecedented outbreaks of PKD have ravaged trout populations in Austria, Germany and Switzerland, and killed salmon and char in Norway and Iceland. All of these outbreaks have been linked to historic low flows and warming water temperatures.

On September 2, 2016, FWP reopened several critical stretches of the Yellowstone to limited recreation, including the popular whitewater sections below the Yellowstone Park boundary. Water temperatures have cooled several degrees, fewer fish are washing up, and there is some sense of relief among area businesses and floaters.

Unfortunately, the root causes of the outbreak remain stubbornly in force. If anything, climate disruptions have been gathering momentum, and many residents fear fish die-offs could become more common in the future.

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