The aim of this study is evaluate water quality of the Aksu River, the main river recharging the Karacaören-1 Dam Lake and flowing approximately 145km from Isparta province to Mediterranean. Due to plan for obtaining drinking water from the Karacaören-1 Dam Lake for Antalya Province, this study has great importance. In this study, physical and chemical analyses of water samples taken from 21 locations (in October 2011 and May 2012, two periods) through flow path of the river were investigated. The analysis results were compared with maximum permissible limit values recommended by World Health Organization and Turkish drinking water standards. The water quality for drinking purpose was evaluated using the water quality index (WQI) method. The computed WQI values are between 35.6133 and 337.5198 in the study. The prepared WQI map shows that Karacaören-1 Dam Lake generally has good water quality. However, water quality is poor and very poor in the north and south of the river basin. The effects of punctual and diffuse pollutants dominate the water quality in these regions. Furthermore, the most effective water quality parameters are COD and Mg on the determination of WQI for the present study. Display omitted •This study aims to evaluate water quality of the Aksu River.•The water quality for drinking purpose was evaluated using water quality index (WQI) method.•The effect of pollutants is dominant on to water quality in the region.•COD and Mg are the most effective water quality parameters.