Nonnative Fish SpeciesNonnative fish distribution and their influence on native fish are not static. While they have not been intentionally stocked since the 1930s, nonnative fish continue to advance into new habitats and hybridize with or displace native fish. Hybridization of cutthroat trout resulting from rainbow trout range expansion continues to be the greatest threat to the park’s remaining native fish populations in waters outside the Yellowstone River headwaters, Yellowstone Lake, and the Snake River headwaters. Not all of the movement by nonnative fish in Yellowstone has occurred naturally. Nonnative lake trout, intentionally introduced by managers in 1890 to Lewis and Shoshone lakes, and introduced (possibly intentionally) to Yellowstone Lake in the mid-1980s, first appeared in angler catches in 1994. The lake trout population expanded and, over the following decade, caused a rapid decline in the Yellowstone cutthroat trout population in Yellowstone Lake. ![]() Lake TroutLake trout prey on Yellowstone cutthroat trout. ![]() Rainbow TroutRainbow trout are native to North America in waters which drain to the Pacific Ocean from northern Mexico to Alaska. ![]() Eastern Brook TroutEastern brook trout was the first nonnative species introduced in Yellowstone—stocked in the (then fishless) Firehole River in 1889. ![]() Brown TroutThe brown trout is the only nonnative fish species in Yellowstone that is not native to North America. ![]() Lake ChubNative to the Missouri and Yellowstone river drainages in Montana and Wyoming, the lake chub is not native to Yellowstone National Park.
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Last updated: June 15, 2020