In Morocco, the Grou River is one of the main rivers that feed the reservoir of the Sidi Mohammed Ben Abdellah dam (SMBA) for the production of drinking water. However, this watercourse is particularly threatened by the problem of pollution, due to the presence of human activities all along its bed. It is in this context that the purpose of this study is to assess the physico-chemical quality of the waters of this watercourse. Four sampling stations that have been selected on the river bed from the entrance of the rural Jmaa Moulblad to the downstream in confluence with the SMBA reservoir. According to a monthly frequency (December 2014 - November 2015), we analyzed 11 physico-chemical parameters (T° of the area, temperature of the area, water temperature (T° of water), hydrogen potential (pH), Electrical conductivity (EC), Redox potential (mV), Salinity (Sal), Total hardness (TDS), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Suspended Solids (SS) and Total Organic content (TOC). The results obtained describe a worrying situation of the state of this watercourse, especially at the station S2 which receives directly the wastewater coming from the rural commune of Jmaa Moulblad without any previous treatment. To remedy this problem, we recommend preliminary treatment of wastewater before being discharged and the implementation of a plan for the sustainable management and management of the River Grou watershed.