Pollution of groundwater and surfaces is a major problem around the world. In Morocco due to population growth, industrial, agricultural and climate change the country is currently experiencing water stress and is expected to experience a water shortage in 2025 (less than 500 m3 / inhabitant / year). In addition, according to the WHO, around 30,000 people per day, approximately 10 million per year, die due to insufficient or poor quality water supply and deplorable hygienic conditions (WHO, 1977). The Sebou river is located in the western region of Morocco, which is a very important agricultural area and therefore experiences high pollution. The purpose of this study is to carry out an updated forecast on its pollution by Urban, Agricultural and Industrial activities. To achieve this objective, several series of samples of the Sebou waters and physicochemical analyzes were carried out (pH, Ca++, Na+, Mg++, Cl-, SO4--, NO3-,…). To verify the hypothesis of pollution of the Sebou river by domestic and industrial wastewaters and by its tributaries, we compared its physico-chemistry with those of Moroccan standards and of the two main rivers in the region, namely the Beht river and the Ouergha river. The results show that Sebou is very loaded with salts (10581 µs / cm; 11g / L). On the other hand, the waters of Beht are less polluted by nitrates (14.34 mg / L) and sulphates (51.51 mg / L) but more loaded with Potassium (55.87 mg / L) and Magnesium. (107.62 mg / L). Finally, the waters of Oued Ouergha are even cleaner than other rivers.