Abstract
Chamo Lake is the third largest rift valley lake and one of the major economic sources for the communities in the Southern region, Ethiopia. The lake's quality is deteriorating due to the untreated wastewater, and sediment inflow resulting in the death of fish was observed during the dry season. The research aims to determine the water quality status using water quality indices, in addition to identifying the reason for the death of fish in the dry season in Chamo Lake. The water samples were drawn from 5 sampling points by composite sampling method during the dry and wet seasons of the year, and we analyzed 22 water quality parameters. Ammonia (14-23.6 mg/l), phosphates (0.30-1.10 mg/l), BOD (25.32-60 mg/l), COD (40-160 mg/l), and chlorophyll (19.64-31.87 μg/L) concentrations were above the permissible limits, and DO (5.20-6.70 mg/l) was below the acceptable limit in the lake as per EPA standards concerning temperature. The values of both the water quality indices of CCMEWQI (13.90-18.40) and NSFWQI (38.59-49.63) indicated that the water quality was "poor" and "bad," respectively. The death of fish might be due to high concentrations of ammonia and nutrients in the dry season.