Paleogeographic reconstructions for the Samarovo, Taz, Murukta, and Sartan glaciations reveal the formation conditions of proglacial lakes dammed by ice in intermontane depressions and valleys of large rivers in eastern Transbaikalia. Middle–Late Pleistocene climate change is reconstructed using spore–pollen spectra from Pleistocene sediments in northern Transbaikalia. The age and lifetime of proglacial lakes are constrained by radiocarbon, thermoluminescence, and varve chronology of their bottom sediments in the periglacial zone. The lake levels remain recorded in sediments produced by deposition and erosion along the former lake shores, as well as in morphology and lithology variations of terminal moraines. A large proglacial lake, with a maximum level of 1020 m, occupied vast areas in Transbaikalia and its surroundings during the Samarovo glaciation. After the glaciers degraded, the Amur River system expanded into the area of closed lake basins in the southeastern Baikal region, including North China and Mongolia. The obtained results have implications for the Middle–Late Pleistocene history of lake deposition.