Due recent years, humanity has faced the problem of lack of clean water for its needs, so the main goals of science are to increase the efficiency of natural resources that would not impair the quality of water. Chemical and biological methods have traditionally been used to assess water quality, but biological methods are more efficient because they are less costly and more informative. Biological control of water quality has a number of advantages over chemical and physical methods, since the grouping of living organisms mirrors all changes in the ecological state of the aquatic environment, while responding to a complex of various factors and pollutants. The method makes it possible to assess the consequences of both permanent and volley contamination. One of the most important biological methods for assessing the ecological state of reservoirs is the assessment of water quality by microbiological indicators, which is the first and most informative component of biota that responds to the allochthonous introduction of organic substances. Microorganisms are involved in optimizing the conditions of the aquatic environment, namely in the building of hydrological and gas regimes and in the self-cleaning of reservoirs, which ultimately determines the quality of water. Therefore, the assessment of the mechanisms of microbiocenosis formation makes it possible to determine the sanitary state of reservoirs by ensuring the functioning of the ecosystem with a bacterial link. The introduction of new technologies should not bring or form any threats to the environment, health and safety of human life, which is why an important task today is to study the impact of microorganisms on the formation of the ecological and sanitary state of aquatic ecosystems.

Key words: microorganisms, aquatic environment, water classes, bioindication, sapidity zones, heterotrophic bacteria.