We studied the sediments of lakes Maselgskoye, Pezhikherye (Baltic Sea basin) and Lyokshmozero (White Sea basin) sampled in March 2022. Measurements of iron content in bottom sediments by titrimetry and mass spectrometry revealed significant amounts of this element in the sediments of lakes Maselgskoe and Pezhikherye, which are due to leaching from soils of the catchment area, mires and intra-reservoir processes. The high concentrations of iron dissolved in the water column of Lake Maselgskoe are also associated with the processes of its anaerobic reduction in bottom sediments. This is confirmed by a decrease in the concentrations of reactive iron in the surface layers of sediments compared to the underlying layers, which distinguishes this reservoir from the other two lakes studied. The process of sulfate reduction in sediments of Lake Maselgskoe was more active than in sediments of the other two lakes, which was reflected in the content and distribution of various forms of sulfur and iron. This fact is associated with an ongoing gradual change of Lake Maselgskoe nutrient status from mesotrophic to eutrophic as a result of nutrient accumulation. Sediments of lakes Maselgskoye and Pezhikherye contained a larger amount of organic matter and sulfur compounds compared to Lake Lyokshmozero. The concentrations of inorganic carbon compounds in sediments of the studied lakes were up to several percent of the sediment dry matter, which is due to the predominance of limestones and marls in the catchment area of the Baltic lakes, and carbonaceous till in the Lyoksmozerо area. The composition (particle-size distribution) of sediments in Lake Maselgskoe is associated both with changes in sedimentation conditions and with processes of erosion of the esker ridge – the White Sea-Baltic watershed.