During fieldwork in March 2022 water samples were taken from three lakes: Maselgskoye, Pezhikherie, and Lyokshmozero. The samples were studied by liquid chromatography, photocolorimetry, conductometry, and potentiometry. Based on the results, the water of these lakes was classified as ultra fresh (average TDS <100 mg/l). The data obtained confirm that water in the studied reservoirs belongs to the calcium hydrogen carbonate class. At all deep-water sampling sites, the water column was stratified by the oxygen content. The oxic-anoxic interface was found at 14–14.5 m depth in Lake Maselgskoye, at 16–16.5 m in Lake Pezhikherie, and at 21–21.5 m in Lake Lyokshmozero. Over the past 10 years since the previous study, the position of this boundary layer has not changed. In lakes Maselgskoye and Pezhikherie, the observed concentration of hydrogen sulfide in the anoxic zone exceeded its MPC for fishery water bodies. The level of this compound in Lyokshmozero was minimal and close to acceptable values. The spreading of hydrogen sulfide throughout the entire water column is prevented by the presence of an oxic zone. The near-bottom layer of Lake Maselgskoye contained a high concentration of dissolved
iron (up to 17 000 μg/l), which is comparable to its content in Lake Svetloye (Primorsky District, Arkhangelsk Region), which is a unique meromictic reservoir of a specific ironmanganese type. According to the content of nutrients, the lakes are classified as mesotrophic. That said, we detected a slight increase in the concentration of phosphates and ammonium in the near-bottom layer of Lake Maselgskoye over a long term, which may point to ongoing active anaerobic mineralization of organic matter.