This study is a preliminary study to determine the origin of the high Mn concentration in the Egirdir Lake water and bottom sediments. The Egirdir lake in the apex of Isparta Angle (SW Turkey) is one of the most important fresh water in Turkey and also used as drinking water source of Isparta city. In the southeast of the lake, Mn concentration is around 196.68 ppb in the lake water and 1134 ppm in the lake sediments, over the maximum acceptable values of World Health Organization and Turkish Standards Institute (0.05 ppm and 0.01 ppm, respectively). Furthermore, in the southwest of the lake, Mn concentration varies between 20.8 – 1.42 ppb in the lake water and 193-227 ppm in the lake sediments. Mn-bearing ophiolitic rocks outcrop around the lake, especially in the southeastern side. Field observations show that anthropogenic-related pollutants are negligible for the Mn contamination in the lake water. We speculate that high Mn concentrations in the lake water may have been resulted from Mn-bearing ophiolitic rocks outcropping in the southeastern side of the lake by the way of water-rock interaction.