Interprovincial Team for the Lower Vistula Cascade, the authors of this project, state that Poland is a country poor in water resources. This situation has been worsening year after year, which is reflected in sinking ground water levels. In recent years water discharges from the Vistula River to the Baltic Sea have been higherthan they should have been under natural conditions. This contributes to further lowering of the ground water levels. The process has to be halted. The most important component of necessary improvement of the water balance at the national level is dam construction and impounding the Vistula River waters. The authors present general principles of a system of impoundments and its advantages as well as the whole concept of the Lower Vistula Cascade.