The standing stocks and instantaneous rates of total, fishing, and natural mortalities of rainbow trout (Salmo gairdneri) and brown trout (S. trutta) in the Green River of southwestern Wyoming were estimated from creel-survey and catch-curve information. Six-year averages for rainbow and brown trout were, respectively: standing stock, 49.6 and 5.2 kg/hectare; yield from the sport fishery, 5.8 and 1.5 kg/hectare; instantaneous total mortality, 1.12 and 0.75; instantaneous fishing mortality, 0.20 and 0.44; instantaneous natural mortality, 0.92 and 0.31; rate of exploitation, 0.12 and 0.30. The primary factor limiting the standing stock is lack of instream cover. Fishing can probably be sustained at current levels by stocking rates of 200 or fewer trout/hectare.