Wild trout in Montana include both native and introduced species. Native species are those that were present in Montana before humans interfered with aquatic systems. Species of the trout family native to Montana include westslope cutthroat trout (Columbia and upper Missouri River basins); Yellowstone cutthroat trout (upper Yellowstone River basin); bull trout (Columbia River basin and Hudson’s Bay drainage in Glacier Park); interior redband trout (Kootenai River basin); arctic grayling (upper Missouri River basin); lake trout (Hudson’s Bay drainage and two isolated lake in the upper Missouri drainage); mountain whitefish (Columbia, upper Missouri and upper Yellowstone River basins); and pygmy whitefish (lakes in Northwest Montana).
All populations of rainbow, brown and brook trout in Montana result from past introductions by humans. All populations of lake trout, except those found in two isolated lakes in southwest Montana and a few that might occur in the extreme northeast of Glacier National Park, also result from human introductions. In addition, westslope or Yellowstone cutthroat trout found outside their native ranges result from introductions by fishery managers or anglers.