The paper presents the results of a study of microorganisms involved in the biofouling of technical and recycled water supply systems of the Novovoronezh nuclear power plant. Sampling was carried out at the following facilities: onshore pumping station (BPS), engine room (MH), spray pool (BB), central pumping station (CNS). The number of microorganisms that make up biofilms varied from 104 to 107 microbial cells in 1 ml. The species diversity at each object is represented by 2 to 3 types of bacteria.