Lake Trout

Two young people inside a boat hold a large fish

The lake trout, introduced to Yellowstone Lake, is one of several aquatic nonnative species having a significant detrimental effect on the park’s aquatic ecology. Here, Student Conservation Association interns hold a large lake trout from Yellowstone Lake.



Lake trout (Salvelinus namaycush) are native to Canada, Alaska, the Great Lakes, New England, and parts of Montana. Lake trout were intentionally stocked in Lewis and Shoshone lakes in 1890 by the U.S. Fish Commission (a predecessor of today's US Fish and Wildlife Service). The species was first documented in Yellowstone Lake in 1994 and evidence from chemical patterns in the ear bones of lake trout captured in the late 1990s indicate that they were introduced illegally from a nearby lake some time in the 1980s. Despite major efforts to remove them by gillnetting, the lake trout are having a significant ecological impact on the native Yellowstone cutthroat trout, an important food for other native animals. Lake trout differ from cutthroat trout as potential prey because they can grow larger, occupy deeper areas of the lake, and spawn in the lake instead of shallow tributaries.

Cutthroat trout comprise about 80% of a mature lake trout's diet. Biologists estimate 41 cutthroat trout are saved each year for every mature lake trout caught. Learn More: Lake Trout Information Continued...


Quick Facts

The Issue

Nonnative lake trout in Yellowstone Lake threaten the survival of native Yellowstone cutthroat trout and species that depend on it.


  • During the time the park stocked fish, lake trout were introduced to Lewis and Shoshone lakes (1890s).
  • Lake trout probably were apparently introduced into Yellowstone Lake in the 1980s and 1990s.
  • In 1994, an angler caught the first verified lake trout in Yellowstone Lake.
  • One mature lake trout can eat approximately 41 cutthroat trout per year.
  • The cutthroat trout population in Yellowstone Lake could fall to 10% or less of historic highs.
  • Many wildlife species, including the grizzly bear and bald eagle, may depend on the cutthroat trout for a portion of their diet.
  • Most predators can't catch lake trout because the trout live in deep water, spawn in the lake, and are large.

Current Status

  • Gillnetting has removed more than 1.7 million lake trout since 1994.
  • Recreational anglers catch approximately 20,000 lake trout each year.


With continued aggressive control efforts, fisheries managers expect to reduce lake trout numbers and lessen impacts to cutthroat trout. Recent monitoring indicates Yellowstone cutthroat trout in Yellowstone Lake are starting to rebound and the lake trout population is in decline.


Did You Know?