The geological record of extreme floods associated with the passage of the strongest typhoons in the last 6620 cal. yr. was first restored for the Sakhalin Island. The cross-section of the Holocene deposits near Dolinsk Town (the watershed in the northern part of the Susunai lowland) was chosen as a natural archive for paleotyphoon activity. The cross-section includes the peat bog with numerous loam layers which formed during the flooding of the swamp during extreme floods. The results of the ecological and taxonomic composition of diatom flora study have been presented with the aim of restoring the evolution of sedimentation environments, as well the analysis of the moisture dynamics and river activity. Peat bog has been formed on the place of the lagoon existed in the maximum phase of transgression in the Middle Holocene. Peat accumulation has begun 6010 cal. yr. BP in brackish-water lagoon. The lagoon had turned into the coastal lake when sea level dropped ~5710-5040 cal. yr. BP. Some bioindicators were re