Beyşehir Lake, Turkey's largest freshwater lake, is also a “Drinking Water Reserve”. In the study, heavy metal (As, Cr, Cu, Ni, Zn, Pb, Cd, Hg, Fe, Al, Mn) concentrations of seasonal lake water and bottom sediment samples were determined to evaluate the heavy metal pollution. Several index methods were applied, and pollution assessments were made using the obtained analysis results of lake water and sediment samples. The average concentrations of the heavy metals in the lake waters are observed as Fe > Al > Mn > As>Zn > Ni > Pb > Cr > Cu > Hg > Cd. When the lake waters were compared with the TS 266 (2005) and WHO (2017) limit values, it was determined that lake waters are below the limit values in terms of the heavy metals. According to index results, all of the lake samples are suitable for use as drinking water in accordance with the heavy metal pollution index (HPI) value, all of the samples are in the “low pollution” class in accordance with the heavy metal evaluation index (HEI) and degree of contamination (Cd) values. In addition, the water average concentrations of the heavy metals in the lake sediments are observed as Fe > Al > Mn > Cr > Ni > Zn > Cu > As>Pb > Cd > Hg. The contamination factor (CF) and enrichment factor (EF) revealed that sediments were considerably and moderately polluted by As, Cr, Cu, Ni, Cd, Fe and Mn and low polluted and/or unpolluted by other metals. The calculated pollution load index (PLI) and Igeo values indicate that lake sediments do not carry a risk of heavy metal contamination.