This study was carried out on El-Sharqe Water Treatment Plant in El-Mansoura city to follow up various types of zooplankton, certain physicochemical parameters and their possible role in the efficiency of the water treatment process. The relative percentage of Protozoa to the total zooplankton ranged from 93.3 to 86.5%  and from 94.6 to 84.9% in the Nile and El-Mansouria influents; respectively while those of rotifers, worms and insect larvae were fewer and more or less similar to each other.  The highest and lowest numerical densities of all these groups were recorded mostly on September 2018 and on Jannuary₂₀₁₈ respectively. Regarding the physicochemical parameters of influent and effluent water samples, it appears that electrical conductivity,  total dissolved solids, dissolved oxygen, and nitrates are higher in the effluent samples as compared with those of the influent ones, turbidity, alkalinity, consumed oxygen, ammonia and nitrites follow an antagonistic behaviour. It was obvious that consumed oxygen, iron, ammonia and nitrite concentrations achieved zero levels in the effluent samples which might give a good indication for the efficient performance of this water treatment plant. It is necessary to mention that nitrates followed a particular behaviour where its concentrations achieved higher levels in the effluent as compared with the influent due to the higher aerial oxidation rate in the latter samples. Statistically, zooplankton particularly Protozoa proved higher positive correlations with temperature, P^H, electrical conductivity, turbidity, nitrites and nitrates where their correlation coefficients (r) ranged mostly between 0.8 and 0.92. On the other hand, the application of the multiple regression proved highly significant relationships between certain zooplankton organisms versus some of the physicochemical parameters (0.002 < P < 0.001).