In Texas, most inland power generating plants are located at reservoirs which are used as a source of water for cooling the condensers. The heated water is returned to the reservoir. Fish populations were studied in three such reservoirs, in an effort to determine the effects of the hot-water discharge. The quantitative methods and analyses used in this study, as well as the results, are evaluated. Fish were captured by hoop net, trap net, gill net, and electro-fishing. Each type of gear was found to be selective for certain species and sizes of fish. Species representation is best when two or more types of gear are used in combination. A significant increase in weight and K-value were observed in both bluegill and white crappie preserved in 10% formalin. The effect of formalin on the length-weight relationship in white crappie varies with size of fish. In a given species, the length-weight relationship varies with sex, maturity, season and size of fish. Coefficients of condition can be compared only for fish of similar length, because variations in lengths created different coefficients of condition. Condition of female bluegill in the area receiving heated effluent ranked third among seven collecting areas in September and seventh among areas in Lake Nasworthy during December. Relative ranking of bluegill and white crappie condition among collecting areas was lower in the effluent area during December than in April or September. The Petersen, Schnabel, Schumacher-Eschmeyer and Chapman-Junge methods performed differently in estimating one white crappie and three bluegill populations, because of behavior and ecology of fish and sampling techniques. The estimated standing crop varied considerably through the year in Lake Nasworthy, where it ranged from 37.4-60.8 and 15.1-52.8 pounds per acre for bluegill and white crappie, respectively. Production estimates of bluegill and white crappie in Lake Nasworthy were -5.37 and 5.52 pounds per acre during the study period.