pondage
водохранилище
(1) The holding back of water for later release for power development above the dam of a hydroelectric plant to (a) equalize daily or weekly fluctuations of streamflow or (b) to permit irregular hourly use of water by the wheels to care for fluctuations in the load demand. (2) In general the holding back of water for later releases. (3) The storage capacity available for the use of such water.
Source http://www.nws.noaa.gov/om/hod/SHManual/SHMan014_glossary.htmstorage reservoir
водохранилище
Reservoir containing water for useful purposes, e.g. water supply, power, irrigation and recreation.
Source EcoLexicon