A cross-sectional study was conducted from November 2015 to June 2016 to determine the occurrence of internal and external parasites in wild fish population of Lake Hashenge and identify the causes of the trends in reduction of fish population. A total of 125 randomly selected fish samples comprising 122 (97.6%) Nile tilapia (Oreochromis niloticus) and 3(2.4%) T. zilli were examined for internal helminthes and external parasites. Overall, 37.6% (47/125) of fish were infested by internal parasites (adults or eggs/larva) while none of them were infested with external parasites. The internal parasites recovered were Clinostomum, Acanthocephalues and Capillaria accounting for 15.2%, 11.2%, and 7.2% of the total infection respectively, while 4% had mixed infection. Moreover, the distribution of parasitic genera were found to be significantly different (p<0.05) with respect to sex, weight, and lengths of the sampled fish, in that females (n=48, 24.8%), fish with body weight 500-1000g (n=89, 30.4%), and length 20-40cm (n=68, 22.4%) were found to be more infected. Most of the respondents (92%) indicated a great reduction in the water and the fish population of the lack from its previous state. All of the respondents have stated that residents of the area wash their clothes in the Lake using synthetic and/or natural detergents and 86% of the respondents believed that Lake Hashenge receives flooding water from nearby uphills and the people use the water from the Lake for small scale irrigation purposes. These findings demand a future focus and stretch of intervention programs for alleviation of the problems facing the Lake before its exhaustion. 76Abreha Tesfaye et al., Ethiop. Vet. J., 2017, 21 (2), 75-91