In Algeria, the water quality in the streams is deteriorating. One of the causes of this environmental pollution is the crop fertilization practices such as the addition of nitrates, eutrophication which causes the degradation of continental marine and aquatic environments from nitrogen inputs. The objective of this study is to evaluate nitrogen pollution in surface waters of the Bouna-moussa Wadi using a physico-chemical approach. This watercourse drains into a watershed mainly characterized by agricultural activities based on irrigated crops and livestock raising sheep and cattle. Fertilizers and livestock waste are important and potential sources of pollution, in the form of mineral and organic nitrogen, having for final destination the hydro-system of this watershed. The analysis of water and soil samples showed that the Bouna-moussa Wadi’s index of organic pollution has gone from one class to another in the different periods. This is mainly due to the lack of control of different discharges and untreated water.