Egirdir Lake is the fourth largest lake in Turkey and located in Isparta province. It is one of the most important water sources in Goller District. Egirdir Lake supplies water to the Egirdir basin and most of the agricultural lands were irrigated through Egirdir Lake and it is also used as drinking water in adjacent provinces. Evaluating the gross-alpha and gross-beta activity concentrations can be accepted as the first step of determining the natural radioactivity level of water. The aim of this study is to investigate the natural radioactivity level of Egirdir Lake surface water by measuring gross-alpha and gross-beta activity concentrations. Study was conducted in two different seasons, in order to evaluate the seasonal effect on results. Seasonal average activity concentrations of gross-alpha and gross-beta varied in a range of 0.0125-0.0345 Bq/L and 0.0750-0.1 Bq/L, respectively. Mean activity concentrations of gross-alpha and gross-beta for seasonal averages were 0.0215 +/- 0.0057 Bq/L and 0.0833 +/- 0.008 Bq/L, respectively. From the measured activities, annual effective dose and excess lifetime cancer risk (ELCR) were calculated. The obtained ELCR results varied in the range of 0.0157%-0.0202% with arithmetic mean of 0.0173%. In addition to that, statistical analyses were carried out in order to investigate the significances of the results. Resultant values exhibited that gross-alpha and gross-beta activities were found to be lower than suggested limits of WHO screening procedure. These results indicated that water consumption-related annual effective dose due to internal irradiation is less than 0.1 mSv/year and the water of Egirdir Lake is of low risk to use as drinking water and also for multiple purposes.