A total of 30 water samples were collected from three industrial localities in Egypt (Helwan “EL- Marazek Bridge", Kaha and Kafr El-Zayat). Ten water samples were collected from each locality near by and at various distances from the outlet of the local industrial establishments. At the same time, 60 Oreochromis niloticus ( O. niloticus) fishes (20 fishes from each locality) were obtained from the same localities of water samples during the period of summer season in 1998, Lead, cadmium, mercury, copper and zinc levels were determined in both water samples and fish flesh by using Atomic Absorption Spectrophotometer, Moreover, the effect of some heat treatments (frying and roasting) On mercury residues in fish flesh was studied, From the obtained data, it was detected that the highest values of lead, mercury, copper and zinc were found in water samples collected from Kafr El-Zayat, while cadi- um was detected at its highest level in water samples collected from Kaha district. On the other hand, it was observed that the highest values of heavy metal residues in fish Samples were found in Helwan, while mercury was detected at its highest level in fish samples collected from Kafr El-Zayat. Moreover, it was found that frying had a stronger effect than roasting in decreasing the residual level of mercury in fish samples. The obtained data indicated a correlation between accumulation of heavy metals in fishes and its concentrations in water. Public health importance and the hazardous toxic effects of these heavy metals as well as the suggestive recommendations to minimize water and fish pollution with these heavy metals were discussed.