One of the debated problems in Pleistocene paleogeography of the Altai region is the extent and time of existence of the last glacier-dammed lakes. For the first time paleontological, mineralogical characteristics, and optically stimulated luminescence (OSL) ages of lacustrine deposits confirm accumulation of ice-dammed lake with depth at least 170 m in Kurai basin during the second marine isotopic stage (MIS-2 according to SPECMAP scale), 16‒19 ka BP. In addition, new information about the ecology and evolution of this Sartanian reservoir is obtained. The consequences of its draining had been less catastrophic than the previous glacial lake outburst floods; however, the lake limited human colonization of the depression in the Late Paleolithic. Drying of the lake determined the formation of the modern river network, including the outlet of the Chuya River along the gorge between the mouths of the Maashei and Belgibash rivers. These new data indicate that the Kurai–Chuya and Uimon depressions had different evolutions at the end of the Late Pleistocene.