Naturally infected Oreochromis species as well as water samples were collected from Elzwaida effluent at Kalubia governorate and examined. The study revealed presences of mixed infection by parasites, bacteria and fungi. 80% of examined fish were suffered from Trichodiniasis. The involved pathogenic bacterial spp. from examined fish were identified as Aeromonas hydrophila, Flavobacteria spp. and Vibrio species. Also Ich thyophonus hoferi was identified in 40% of examined fish. The clinical signs among examined fish varied according to the severity of infection which was summarized as detached scales, black coloration, superficial ulcers, fin & tail rot and or hemorrhagic signs on body surface. Post-mortem findings varied according to type and severity of infection summarized as hemorrhagic signs in internal organs with congested blood vessels of intestine and mesentery.