The western pearlshell occurs near the Continental Divide on both sides. They are found in trout streams and rivers west of the divide, as well as in sand, gravel, and between cobble and boulders of the Missouri headwaters. The western pearlshell often are found in drainages with the westslope cutthroat trout (its native fi sh host). Conservation concerns include: habitat degradation and fragmentation (e.g., dams); point and nonpoint source pollution; and stream deterioration due to high sediment loads from agricultural runoff. Conservation strategies include: considering a management plan for the western pearlshell or including it in another comprehensive taxonomic plan; enforcement of regulations addressing dumping of pollutants into waterways; and restoration of stream channels and riparian areas.