Water quality describes the condition of the water, including chemical, physical, and biological characteristics, usually with regarding to its suitability for a particular purpose. The present study describes the environmental conditions of Mahmoudia canal which are the main water source for Alexandria and Behiera governorates. Water samples were collected from ten sites along the Mahmoudia canal in the year 2018 for study the seasonal variations of the water quality parameters (physicochemical and biological parameters). The measured physicochemical parameters include; (Turbidity, Temperature, pH, Electrical Conductivity, Total Dissolved Solids, Total Suspended Solids, Total alkalinity, Total Hardness, Nitrate, Nitrite, Ammonia, Sulfate, Phosphate, Dissolved Oxygen, Biological Oxygen Demand, Chemical Oxygen Demand, Chlorinated pesticides and some heavy metals). Phytoplankton and Zooplankton were examined as biological parameters. The values of average water quality index (WQI) of Mahmoudia canal ranged from 75.01 (poor water quality) to 132.57 (very poor water quality). According to the results of Cluster analysis, six statistically significant clusters were formed. Three groups of phytoplankton were recorded which, the annual maximum density of phytoplankton recorded in Town of Abou Hommos, while the lowest recorded in site Zawyet Ghazal Village. The highest density registered in winter (3460.2 U/ml), while the lowest density recorded in summer (831.6 U/ml). In addition to six zooplankton groups were quantified in the analysis of the samples from ten sites, the highest density listed in summer (6000 ind./m3) ,although the lowest listed in winter (3200 ind./m3).