The ecological state of Lake Komsomolskoye (Kazan) in the fall-winter season was evaluated using bacterioplankton and bacteriobenthos indicators. In the summer of 2019, comprehensive actions were taken to clear the lake bottom of silt deposits. As a result, a significant improvement in hydrochemical parameters of the water was observed duringthe subglacial period of 2020 compared to the previous year. Indicators of microbial water quality conformed to Roshydromet regulatory requirements. Due to the high sulfate concentration in the bottom layer and especially in the benthos, mass development of sulfate-reducing bacteria took place. During the ice-covered period, purple phototrophic and colorless sulfur bacteria occurred in the surface water layer. Oxygen depletion in lake water can cause mass development of anaerobic purple bacteria, as well as a change in surface water transparency and color. Additional aeration of the Lake Komsomolskoye hydroecosystem with a sufficient amount of oxygen in winter can improve the hydrochemical composition and eco-trophic structure of the microbial community. These studies are part of the system of observations of urban water bodies designed to develop a program of actions for maintaining the ecological well-being of their ecosystems.