We defined relations of environmental variables and fish community features to statistics of samples of rainbow troutOncorhynchus mykissfrom lakes and reservoirs in Wyoming. The mean length of rainbow trout in gill-net samples was most strongly related to physical features, including elevation, measures of water chemistry, and lake morphology. Indices of abundance and biomass of rainbow trout were related to the proportion of other fish species in gill-net samples, as well as elevation, water chemistry, and lake morphology. Environmental gradients associated with changes in elevation appeared to have substantial influence on the population structure and abundance of rainbow trout in lakes and reservoirs in Wyoming.