Mariout Lake is now one of the most heavily polluted ecosystems in Egypt and a major source of pollution to the Mediterranean Sea through El Mex Bay. This study was carried out from February 2018 till January 2019, nine sites distributed in the Lake different basins to assay water quality properties, planktons, and bacterial community in water, sediment, and O. niloticus organs. Water quality results revealed that salinity ranged from 2.77 to 5.80 g/l. Total alkalinity fluctuated in range 230.00- 480.00 mg/l and this not well for fish growth. Nitrite and Nitrate were ranged between 0.024- 0.321 mg/l and 0.096-1.541 mg/l, respectively. Most of these values are within the safe limits for fish health. Ortho- Phosphateconcentration fluctuated between 0.054 to 0.405mg/l. Phytoplankton community results take the following order Cyanophyta> Bacillariophyceae> Chlorophyceae> Euglenophyta. On the other hand, Copepoda and Cladocera were the most remarkably abundant zooplankton group than Rotifer and Ostracoda groups. The bacteriological examination showed that the main basin (6000 feddan) showed the highest bacterial load (TBC, CF, E. coli & Vibrio cholera) in water, sediment, and O. niloticus organs than other Lake basins. Where, TBC, CF, E. coli & Vibrio cholera recorded higher values in sediment and water than O. niloticus organs. The results of bacterial load in water and O. niloticus organs exceed the permissible limits which can cause a health risk for fish and consumers.