Westslope cutthroat trout seek out gravel substrate in riffles and pool crests for spawning habitat. Westslope cutthroat trout also require cold water, although it has proven elusive to define exact temperature requirements or tolerances. Juvenile cutthroat trout overwinter in the interstitial spaces of large stream substrate. Where the species range overlaps, westslope cutthroat trout are often found in the same streams as bull trout and mountain whitefish. There are four primary reasons for the decline of this species.
Habitat loss is considered to be a widespread problem.
Cutthroat trout have declined due to poor grazing practices, historic logging practices, mining, agriculture, residential development and the lingering impact of forest roads. Fish have been unable to use countless miles of spawning habitat due to dewatering of streams for irrigation and because of barriers created by dams and road culverts. Non-native species have also taken a huge toll on westslope cutthroat trout. Experience shows that once brook trout dominate a stream, cutthroat trout never regain it. Other non-native species like lake trout, brown trout and northern pike prey on cutthroat trout.