Nonnative Fish Species
Nonnative 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.
Last updated: June 15, 2020