Garaet Hadj-Tahar wetland is part of the Guerbes-Sanhadja complex in northeastern Algeria, covering an area of 230km². The aim of this study was to assess the physicochemical quality of the surface waters in this Garaet. Sampling was carried out at two different sites over a 12-month period (November 2021 to October 2022). The results of the physicochemical analyses expressed a very low dissolved oxygen (0.56 to 0.94mg/ l). The concentrations of nutrients, particularly nitrites and orthophosphates, were extremely high (0.94 and 7.63mg/ l, respectively), indicating that the water body is highly polluted. High concentrations of chlorides and magnesium, with values of Cl⁻ = 1023 mg/l, Mg²⁺ = 108 mg/l, are attributed to the leaching of existing geological formations. PCA and HAC analyses confirm the degraded quality of water in Garaet Hadj Tahar due to agricultural pollution. This organic pollution is highly excessive where the OPI reached its maximum (174) during the intensive agriculture activity, in October. The protection of this wetland is a major concern and requires the rational use of chemical fertilizers and the treatment of wastewater discharged into this natural ecosystem.