Historically, Yellowstone Lake supported a population of cutthroat trout estimated at up to 3.5 million fish. In the middle 1990s, that population had declined to 2.5 million. Most recently, fisheries biologists believe the lake’s cutthroat population is now between five and ten percent of its 1995 level, or approximately 125,000 to 250,000 native fish. The culprit in the decline of the cutthroat trout is another trout, the lake trout, a non-native species likely introduced to Yellowstone Lake in the 1980s. No one is certain how the lake trout found its way into Yellowstone Lake. It may have been dumped illegally into the lake by an ignorant fishing enthusiast who hoped to create a lake trout fishery where one had never existed before. It is also possible the fish entered the lake during the Great Yellowstone Fire of 1988. Helicopters equipped with water buckets pulled water from Yellowstone Park’s numerous lakes to douse the many blazes. Crews may have inadvertently lifted lake trout out of Lewis Lake and then unknowingly carried the lake trout eggs or fingerlings into Yellowstone Lake when they went in to refill their buckets there. However the fish found their way to the deep, cold caldera lake, it is now apparent to all that they have thrived there. Lake trout have fed for decades on cutthroat trout. Biologists estimate that an adult lake trout can eat on average 41 cutthroat per year. The National Park Service wants to reverse the decline of the Yellowstone Lake cutthroat.

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