Bottom sediments from Lake Okunozero, located in front of Syamozero marginal formations, were analyzed to better understand the degradation conditions of the Last Glaciation in South Karelia at the Neva (Syamozero) stage and to assess the effect of climate on environmental changes. Paleogeographic reconstructions are based on the study of lake sediments using an integrated approach, which comprises spore-and-pollen, diatom and radiocarbon (14C) analyses. More evidence was obtained for the Late Glacial deposition pattern, the environmental conditions and evolution dynamics of the proglacial ice lake directly contacting the ice margin and of vegetation in that period. For the first time, Lake Glacial sediments were found to contain over 30 redeposited marine diatom alga species and varieties, not reported earlier from rock sequences of that period. The lake separated from the periglacial water body at the end of the Late Dryas. Its evolution after separation from the proto-Onega was traced, evolution stages were recognized, and more light on was shed the paleogeographic conditions in the surrounding area. The vegetation dynamics from the Alleröd to the present day was reconstructed. In the Late Glacial Period the study area was occupied by tundra dwarf birch-true moss, sagebrush-wormwood periglacial-steppe and forest-tundra paleocommunities. Meadow-like tall-herb communities and birch forests with an admixture of pine appeared in the Preboreal. In the Boreal time, light-coniferous pine forests with an admixture of birch occupied the area, to be replaced in the Atlantic period by pine-spruce forests with the participation of broad-leaved species. Since the Subboreal, spruce and pine-spruce forests have prevailed in the study area. We observed that diatoms were missing from some horizons in almost every paleoclimatic period and suggested possible explanations for these gaps.