The composition of microbial communities in coastal zones in the area of Kislogubskaya tidal power plant (the Barents Sea) and near Saint Petersburg Flood Prevention Facility Complex in the Gulf of Finland (Baltic Sea) was studied. The enrichment and pure cultures of microorganisms of various groups (sulfate-reducing, sulfur-oxidizing, nitrifying, ammonifying and iron-oxidizing bacteria) have been isolated, their cultural and physiological-biochemical properties, as well as their ability to induce corrosion of different materials used in the construction of hydraulic structures, have been studied.