Water Quality Index (WQI) was applied in Dokan Lake, Kurdistan region, Iraq using ten water quality parameters (pH, Dissolved Oxygen, Turbidity, Conductivity, Hardness, Alkalinity, Sodium, Biochemical Oxygen Demand, Nitrate and Nitrite). The relative weight assigned to each parameter ranged from 1 to 4 based on the importance of the parameter for aquatic life. The results indicated that water quality of Dokan Lake declined from Good in the years