Clostridium perfringens (CP) was evaluated as an additional indicator in assessing impacts and sources of microbial pollution in the Idaho-Utah Cache Valley . Point , nonpoint, river water, and animal fecal samples were analyzed for CP, total coliforms, fecal collforms, and fecal streptococci. Monthly river samples consistently contained <20 CP/100 mL , but concentrations of the other indicators varied significantly by location and date. Two sample stations consistently had CP concentrations greater than 20 / 100 mL . One of these stations was influenced by an upstream wastewater discharge . Chlorinated effluent from this trickling filter plant contained greater than 103 CP / 100 mL, but met a 400 FC/100 mL discharge standard. A consistent decrease in CP concentrations in samples taken downstream from this wastewater source were fo und, despite significant impact from adjacent nonpoint pollution. Lagoon and oxidation ditch wastewater effluents sampled contained <20 CP/100 mL. Nonpoint sources sampled (e.g . , cattle feedlot runoff) contained <20 CP / 100 mL and 102-104/100 mL coliforms and fecal streptococcus. Cattle, horse, and sheep feces analyzed contained 104-107/g coliforms and fecal streptococcus, but less than 102 CP/g. Nonpoint pollution from such animals may contribute significant coliforms and streptococci but not CP. Wastewater treatment effluents may or may not contain elevated levels of CP depending on factors such as wastewater residence time and particular treatment process employed. The occurrence of relatively high, i.e., >102 CP/100 mL, in areas impacted by nonpoint sources may suggest a municipal wastewater input. Coliform and streptococci indicators may not be able to distinguish municipal or domestic microbial loading in the presence of nonpoint source interferences in many circumstances.