In this work, we investigate the hydrochimy of surface water of the Senegal River (the Mauritanian delta of the city of Rosso). After several years of domestic exploitation: agricultural and industrial one, besides the climate changes in the area, it is interesting to make sure of the quality of water. With this intention, we tried to carry out a physicochemical evaluation, to have an idea on the probabilities of pollution and the effect of the seasonal variation of the climate on water of this river. For that a sampling was carried out during every season of 2015 at the five stations on the axis of the river at the city of Rosso. The followed physicochemical parameters are : T°C, pH, C.E, the total hardness (TH), Ca2+, Mg2+ , Na+, K+ , NH4+, CL-, NO2-, NO3-, HCO3-, CO2, SO4--,TA, TAC and suspended matter. These measures comprise volumetric analysis, spectroscopic, Potentiometric. Statistical exploitation of the results and their comparison with the European standards of potability of water has shown that there is a true deterioration of the quality of water of the Senegal River. The content of nitrite varies between 0.13 mg/l and 1.6 mg/l with an average about 0,55mg/l which exceeds the standard (0.1 mg/l).The content of bicarbonate varies between 18 mg/l and 61 mg/l with average value36, 14mg/L exceeds the standard (30 mg/l).The content of carbon dioxide varies between 6.94 mg/l and 28.45 mg/l with average value 17.26 mg/l exceeds the standard (10 mg/l). A quality control of water of the Senegal River must be required and updated in particular the reduction of the domestic and industrial effluent of the factories located at the shore of this river.