The aim of this work was to present the results of fragmentation the Prut River’s ecosystems within Moldova as the first step in valuation of the ecological impacts of Costești-Stânca dam and hydropower plant (HPP) operation. The environmental consequences of dams are numerous and varied, including the direct and indirect impacts on biological, chemical and physical properties of riverine and riparian ("stream-side") ecosystems. In our case, the riparian ecosystem are understood as a stream channel between the low- and high-water marks plus the terrestrial landscape above the high-water mark where vegetation may be influenced by elevated water tables or extreme flooding as well as by soil water capacity. Riparian areas are particularly sensitive to variation in the hydrological cycle and thus serve as a good indicator of any change in the environment caused by dam and hydropower plant operation. Moreover, riparian processes have a central ecological role in most landscapes, while the riparian ecosystems offer habitats for many species, serve as filters between land and water, and pathways for the dispersing and migrating organisms; they also provide with many economic and recreational values. The degree of HPPs and dams influence on the ecosystems depends mainly on three stimuli: - Change in the hydrological regime and the state of inundated riverbed complexes downstream the dams; - Transformation of aquatic ecosystems above dams; -Fragmentation of a river basin due to blocking by dam the flow of energy, matter, nutrients and biological objects species and populations. Identification of areas, which provide water-related ecosystem services in the Prut River basin, proceeded from the principles of the European Water Framework Directive. In accordance with this document, Moldova is located within two ecoregions: Pontic Province (12) and Eastern Plains (16). The Prut’s riparian ecosystems are located at altitudes below 200 m. The Prut basin dominant geology is siliceous; in the northern part the calcareous rocks predominate. On the whole, in the Prut floodplain six elements were identified, which include both individual reaches and other water bodies. From these elements, the four are located below the Costeşti-Stânca dam. The territory under study includes the following ecosystems (more than 730 plots): water (12.8%), forest (17.6%), grassland (50.9%), wetlands (11.6%), perennial plantations (0.5%), and built-up areas (6.6%).Within this territory there is Ramsar site “Lower Prut Lakes”. A large part of this site is included in the Lower Prut biosphere reserve. The presence of natural floodplain lakes with area of up to 850 hectares is a principal characteristic of the Lower Prut basin. For the selected elements (sub-basins), the fragmentation coefficients were calculated as a ratio of their areas to their perimeter. The fragmentation results reflected a high mosaic structure and degree of ecosystem diversity. Acknowledgement: The current work was realized in frames of the Joint Operational Black Sea Programme 2014-2020, the Project BSB 165 „HydroEcoNex”, with the financial assistance of the European Union.