Systematic environmental investigations of the Southern Buh flooded areas as preserves of the unique natural vegetation have been conducted. Among the marsh river territories, the largest Varyushino-Kovalevskyi marsh area covering about 1000 hectares has been discovered. It belongs to the group of natural riverlake formations of the eutrophic type (the biomass is estimated as 1050-1120 gm/season/m2 ). It has been revealed that the diversion of the watercourse hydrological regime and the marsh siltness intensify the processes of biomass production solely at the expense of macrophytes, which dramatically inhibits the cycling of substances in the marsh ecosystem. Marsh amphiphytic vegetation has been naturally found within the marsh biotopes of continued flowage and partial flooding with a rapid change in water rate on silt and sandy sediments. It is represented by free-flowing, submersed and emergent hydrophilic plants, which, in the conditions of marshlands, are displaced by hygrophytic eurybiont species. In the course of geobotanical explorations of vegetation in Kovalevskyi marsh area, natural rare vegetation groups of Nymphaeaceae, including floating fern (Salvinia natans), listed in the IUCN Red List, were identified, which increases the sozological value of this territory.Generalized ecological and phytocenotic studies indicate that in general, the ecotope hydrological regime is a determining factor for spreading of the marsh amphiphytic vegetation. Current growing aridity of the climate and anthropogenic pressure on the river floodplain have caused the diversion of the watercourse hydrological regime by creating critical conditions for the vegetation of hydrophilic plant
marsh, amphiphytic vegetation, the Southern Buh flooded areas, ecological and hydrological changes