Abstarct: Abstract In general, any dam can be considered completely water seal, and there is seepage water in all dams especially in karst regions. Kowsar Dam with a reservoir volume of about 580 million cubic meters has been built in Kohgiluyeh and Boyer Ahmad province at Tang Dok on Khairabad river. The study area is the folded Zagros plain region with a folded structure. The river has carved a deep, V-shaped and almost symmetrical valley in the limestone units. All the faults are mostly parallel to the dam axis and are perpendicular to the river. The bedrock and the abutments are composed of the limestone of the Asmari formation. Geological outcrops in the studied area include Pabdeh, Asmari, Gachsaran, Mishan, Aghajari, Bakhtiari, and quaternary sediments. After the construction of the dam, the plans regarding the body, foundation and abutments of the Kowsar Reservoir Dam were discussed. In this study, It has been tried to investigate the issue of signs of abutments leakage potential by studying the hydrogeology of the region. The changes in the water level of the reservoir are used as an important part of the amount of seepage and the investigation of the downstream springs in terms of quantity and quality, as well as the type and location of their emergence. In completing the studies the qualitative relationship between reservoir and downstream water resources has also been investigated in different periods. The changes in the groundwater level using observation wells, determining the type of flow direction in the dam abutments, calculating the balance of the reservoir and the water catchment basin of the spring, and qualitative changes in water sources show that the reservoir has a significant connection with the lower springs. The evaluations show that a significant volume of the discharge of the springs in downstream is from the reservoir and the process of quantitative and qualitative changes in the reservoir has a direct effect on the downstream discharges.