Résumé: The scarcity of freshwater resources in the transboundary region of Sidi Fredj, located in the Souk Ahras province (northeastern Algeria), is exacerbated by the high salinity of groundwater, which exceeds 5 g/L. This elevated salinity is primarily attributed to the leaching of Triassic formations rich in gypsum and evaporites. To meet the growing demand for drinking water, two reverse osmosis desalination plants have been commissioned, supplied by boreholes AOB2 and AZ2. However, the brine discharges generated by these treatment units pose a potential threat to the receiving aquatic environments. This study aims to assess the impact of brine discharges on the water quality of two receiving streams: Oued Mellègue and Oued El Maleh. The adopted approach is based on a comparative monitoring of key physicochemical parameters, including temperature (T), hydrogen potential (pH), electrical conductivity (EC), total dissolved solids (TDS), and concentrations of sodium ( Na+), chloride ( Cl−), and sulphate ( SO4 2−), both in the brine effluents and in the stream waters. A bimonthly monitoring campaign was conducted to evaluate the temporal variation of selected indicators (EC, Cl−, SO4 2−) upstream and downstream of the discharge points. The results reveal a significant increase in the mineralization of water in the receiving streams, directly linked to the brine effluents, specifically, Electrical Conductivity (EC), total dissolved solids (TDS), sodium ( Na+) and chloride ( Cl−), the results indicate that Electrical conductivity (EC) increases from 3500 to 6500 μS/cm upstream to values ranging between 3600 and 7100 μS/cm downstream, reflecting a rise in salinity attributable to brine discharges. Multivariate statistical analysis supports these findings and identifies sulphate as the primary contributor to the mineral load in the impacted waters. These results indicate a marked deterioration in surface water quality, with exceedances of Algerian water quality standards, suggesting a potential risk to local aquatic ecosystems. Further ecological investigations, including biological assessments, are needed to confirm this hypothesis.