This study aimed to assess the water quality of Oued Ain bayda (Saida, ALGERIA) and identify the types of pollution present. Monthly sampling was conducted at three stations (S1, S2, S3) to analyze the physicochemical parameters including temperature, pH, electric conductivity, biochemical oxygen demand, dissolved oxygen, nitrite, nitrate, chloride, ammonium, suspended solids, sodium, fatty oils, and turbidity. Results indicated that temperature ranged from 10°C to 19°C, pH ranged between 7.5 and 9, and conductivity ranged from 10 to 23 μs/cm. Biochemical oxygen demand ranged from 8.38 to 15.30 mg/l, while dissolved oxygen ranged from 1.58 to 2.9 mg O2/l. Nitrite ranged between 1.50 and 2.03 mg/l, and nitrate ranged between 46 to 55 mg/l. Chloride ranged between 78 to 81 mg/l, ammonium ranged from 1.68 to 2.36 mg/l, suspended solids ranged from 155 to 195 mg/l, sodium ranged from 7 to 7.60 mg/l, and fatty oils ranged from 96 to 116 mg/l. Turbidity ranged between 8 to 17 NTU, with a significant increase observed in winter (December to January) in 2022. The summer (especially August) recorded the highest means for all parameters except for turbidity. Pollutants found in Oued ain bayda were of various origins, including industrial, chemical, and agro-food.