This research is to evaluate the physicochemical quality of surface waters Oued Moulouya relationship with his tributary Oued Sebra. These waters are threatened by the extent of urban and industrial discharges from the city of Zaio. Water samples were taken from five stations on the lower part of the Moulouya and a station on the left bank tributary of the Oued Sebra. This study focused on the distinction of physic-chemical water parameters (temperature, pH, CE, MES, turbidity, O2, DBO5, DCO, PO4 3- , Pt, NH4 +, NTK). In order to establish a relationship between these parameters and to better assess the impact of human activities on the quality of surface water, a statistical analysis PCA (Principal Component Analysis) was applied to all of these parameters in the wet season and dry season. The Explanatory Analysis by Principal Component Analysis (PCA) of data physicochemical, allowed us to identify correlations between the different parameters and differentiate a typology of water quality in the study area. The results show an alarming situation of the quality of the waters, especially of the Oued Sebra, that receives industrial waste from the city of Zaio. We are witnessing an increase in levels of DBO5, DCO, MES ... NTK, and a decrease in dissolved oxygen levels, especially in the summer period (period of sugar activity). The explanatory analysis (PCA) showed an inter-station variability and corroborated the results of the descriptive analysis.