The aim of the study was to detect the detrimental effects of water pollutants on gonads structure of wild tilapia, O. niloticus. A total of 209 wild fish were collected from Lake Manzala during the spawning season, summer of 2018. According to the sex ratio and the body weigh fish were divided into four male and three female groups. Anatomical measurements and histological examination were performed for all specimens. Data reveled that sex ratio of collected fish was 74.64 and 25.36 for male and female, respectively. Body length for males was ranged from 11.6 to 19.5 cm and from 13.6 to 18.58 cm for females. Body weight was ranged from 30.05 to 139.73 g and from 39.60 to 125.13 g for male and female, respectively. Microscopic inspection illustrated that fish gonads both testes and ovaries were affected as indicated by the deterioration and degeneration of seminiferous tubules and germinal epithelium as well as the existent of testis-ova and testis fibrosis, and in female by increasing the percentage of atretic follicles and reabsorption of vitellogenic oocytes. The data reflected the prominent changes in male and female gonadal structure, which could be attributed to the accumulation of pollutants and prolonged period of exposure. This may affect the future spawning seasons; the rate of sex cycles or reproductive failure eventually. Such changes can damage the economic revenue of Lake Manzala. Thus, it is recommended to increase water circulation through inlet purgation to attenuate pollutants and restocking the lake.