The Westslope cutthroat has teeth under its tongue, on the roof of the mouth, and in the front of the mouth. These cutthroat reside in both headwaters lake and stream environments (typically migrating into streams to spawn). They feed largely on insects and, in lakes, zooplankton.
Adult Westslope typically display bright yellow, orange and red colors, especially among males during the spawing season. And typical of the cutthroat species has a bright orange marking beneath the jaw. Unique characteristics of Westslope include irregular shaped spots on the body and fewer spots below the lateral line (except near the tail).
The Westslope cutthroat trout has the name Oncorhynchus clarki lewisi, in honor of Meriwether Lewis and William Clark who led the First American Expedition into the Northwest United States. Lewis and Clark discovered the Westslope cutthroat at Great Falls of the Missouri in what is now Montana.
Westslopes are native in northern Idaho's and British Columbia's upper Columbia system and northern tributaries of the Snake River, but not the Snake River's main stem to the south. Across the Continental Divide, Westslopes are native to the upper Missouri River, Milk River and North Saskatchewan River, but not the Yellowstone River to the south. However there is a remnant population of Westslopes in Oregon. Small populations persist in upper tributaries of the John Day River in the Strawberry Mountains.