Egirdir Lake is an important water resource protected by special regulations. The lake is located in the southwestern part of Turkey. The water quality of the lake is affected by the surface and groundwater sources coming from the basin. The quality of water in the study area is threatened by agricultural activities, anthropogenic effects and industrial areas. As an important water resource, both water quality and protection from contamination are serious issues. The present study aimed at examining the quality and contamination of surface and groundwaters in Senirkent-Uluborlu basin which is located in the surface discharging area of Egirdir Lake. It is concluded that there is a water recharge from the basin to Egirdir Lake with meanly 25,680,000 m(3)/year surface water and meanly 33,220,000 m(3)/year groundwater flows. Hydrogeological structure of the basin has been explained in the study. The hydraulic relation of aquifers with lake has been proven and the water quality has been evaluated by investigating the hydrogeochemical properties of groundwaters in the basin. Groundwater samples have been taken from 17 separate locations chosen representatively by taking into consideration the type of land usage in the basin. The hydrogeochemical analysis results of the water samples have been evaluated according to different kinds of diagrams and statistical methods and it has been seen that the waters in the basin are of CaMgHCO3 water type. According to the Stuyfzand Hydrogeochemical Classification Systems, the water of the basin is of G2-3-CaHCO3 + water type. The results of chemical analyses showed high concentrations of NO2 and NH4 which must be nil. In the study area, agricultural activities are probably the most significant anthropogenic sources of NO2 and NH4 contamination in groundwater. The high concentration values of NO3, Zn, Mn and Fe which were found in some water samples exceeding the safe limits of drinking purposes resulted from anthropogenic pollutions. It is recommended that more precautions have to be considered to protect the basin water from contamination.