Shallow North-Western part of the Black Sea accepts ¾ of total rivers inflow into the Sea. This area is significantly affected by discharge of four biggest rivers flowing into the Black Sea. These Rivers are Danube, Dniester, Dnieper and Southern Bug. In 20th century on these plains rivers (except for Southern Bug) have been constructed power plants with big artificial reservoirs. These actions dramatically changed hydrological, hydrochemical and ecological regimes of these rivers especially for Dnieper as most overregulated. Of course, hydropower energetic, water use and climate changes cause general decreasing of water discharge of the rivers. Worrying news about plans of Ukrainian government to build several reservoirs on upper Dniester for hydropower prompt us to predict the changing in hydrochemical regime in the system River-Estuary-Sea.