The paper presents and discusses the results of the lithological, chronological and bio­stratigraphic study of the sediment sequence on Bolshoy Klimenetsky Island, the larg­est island within the Kizhi Archipelago. Inferred changes in sedimentation environments are related to the lake-level changes of Lake Onego in the Late and Postglacial times. At the earliest stage, the sedimentation took place in the Onego Ice Lake, when the lake level exceeded 80 m at the study site. Seasonally laminated clays accumulated at the bottom of the ice lake. Diatoms were substantially limited in both essential nutrients and light due to increased water turbidity. With the regression of the Onego Ice Lake ca. 11300 yrs BP the formation of micro-laminated clays started. The Lake Onego level drop prior to ~6500 yrs BP, presumably at the Early Holocene, resulted in the erosion of the older sediments. This was followed by the establishment of shallow-water coastal environments favoring the accumulation of sandy sediments and flourishing of benthic diatoms. At the following stage, low-energy environments gradually formed as a result of decreased hydrodynamic action and possibly some water-level rise due to increased climate humidity in the mid­Holocene. Silty sediments with a higher proportion of planktonic diatoms accumulated at the small shallow bay that existed at the study site. ~7000 yrs BP the Lake Onego lev­el was below ~40 m. As the regression proceeded, ~6500 yrs BP the Lake Onego level dropped to ~36-37 m, and organic sedimentation started in the sheltered bay, where epiphytic diatoms prevailed. ~6100 yrs BP the Lake Onego level dropped further to below ~36 m, resulting in the isolation of the study site and the onset of peat formation.