This study aimed to display the microalgal distribution, diversity, and their relationship to water quality at ten selected stations (S1 to S10), North Damietta, Egypt. The water physicochemical parameters as well as the qualitative and quantitative investigations of microalgae were performed seasonally from Autumn 2021 to Summer 2022. Salinity values varied between 0.4 gL-1 at River Nile Dam (S6) to 400 gL-1 at Al-Diba pond (S10). The highest concentrations of ammonia and nitrite (3.7 mgL-1 and 0.5 mgL-1, respectively) were recorded at S1 while the highest concentration of nitrate (5.37 mgL-1) was estimated at S9. Although the orthophosphate concentrations were low, total phosphorus values were acceptable. A total of 137 microalgal taxa, belonging to 7 algal groups, were microscopically identified. Diversity index values indicated that the water status varied between mildly polluted at River Nile (S6) and heavily polluted water at stations 3, 5, 8, 9, and 10. The findings concluded that the species diversity decreases by increasing the pollution as well as increasing salinity. Furthermore, the results confirmed that high species diversity coincides with low dominancy and vice versa.