Fish Deaths in Montana's Yellowstone River Tied to Warming Waters

A parasite that is killing tens of thousands of fish is blamed on low stream flow and warming waters, both impacts of climate change in the West.

An outbreak of fish-killing disease along a 100-mile stretch of the Yellowstone River in Montana may be the latest sign that mountain stream ecosystems are being disrupted by climate change.  Scientists point to warmer, slower rivers as a likely cause of the mass fish mortality.

Since Aug. 12, the Montana Department of Fish, Wildlife and Parks has counted 4,000 dead mountain whitefish, along with smaller numbers of rainbow trout, Yellowstone cutthroat, longnose suckers, sculpin and longnose dace.  The agency estimate that tens of thousands of fish may be dead and they closed the 100-mile segment to recreation to reduce impacts to fish.  This is happening along a river that's an economic mainstay for nearby communities and thought of as a relatively healthy, undammed river.

The culprit is a microscopic, capsule-shaped parasite called Tetracapsuloides bryosalmonae.  In slower, warmer water—both impacts of climate change—the parasites thrive, while the stressed fish grow weaker.  More and more of the spores invade the fish through their gills, eventually overwhelming their hosts.

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