An off-stream reservoir is a reservoir that is not located along a natural watercourse and is instead supplied by a pipeline, aqueduct or the redirection of adjacent watercourse. An off-stream reservoir may also serve as dry reservoirs, that is, they assist with flood mitigation and do not hold water until such time as a major flood event occurs. Most off-stream reservoirs are impounded by embankment dam walls made from rock-fill or earth-fill.

Off-stream reservoirs may assist in limiting the ecological impact of a reservoir.

Examples of off-stream reservoirs

• San Luis Reservoir the largest off-stream reservoir in the United States. Although it is located on a small stream, it gets the vast majority of its water from the California Aqueduct by pumping aqueduct water up-hill to the reservoir

• Sites Reservoir a planned off-stream reservoir in California

• Cardinia Reservoir and several other reservoirs that comprise the Melbourne Water supply system, in Australia

• Springbank Off-Stream Storage Project completed in 2025 for flood mitigation, located in Alberta, Canada, the dry reservoir is fed by a diversionary canal from the Glenmore Reservoir

See also

• Types of dams

• Environmental impact of reservoirs

References