Hydropower: reservoirs, rivers and pumped storage
Distinguish hydropower types, water availability, installed capacity and environmental questions when reading hydroelectric plant records.
By Power Stations Worldwide · Reviewed 28 September 2026 · Editorial approach
What is reservoir hydropower?
Reservoir or impoundment hydropower stores river water behind a dam and releases it through turbines to generate electricity. Stored water can support timing choices, but reservoirs may also serve other purposes. The power station is only one part of the water-management system associated with the site.
Sources: US Department of Energy: Types of hydropower plants
What does run-of-river hydropower mean?
A diversion or run-of-river installation channels river flow through a waterway and turbine arrangement. Some designs do not need a dam. The label should not be used to infer unlimited flexibility or a specific storage volume; those depend on the actual facility and its permitted operation.
Sources: US Department of Energy: Types of hydropower plants
Is every dam a hydroelectric power station?
No. Dams can serve water supply, flood management, irrigation or other purposes without generating electricity. Seeing a reservoir on the basemap is therefore not enough to identify a power station. The atlas requires a sourced generation record rather than converting visible dams into assumed generating assets.
Sources: US Department of Energy: Types of hydropower plants
Is pumped hydro the same as conventional hydropower?
No. Pumped storage uses electricity to lift water before recovering energy during discharge. Conventional hydro relies on naturally supplied water. Some sites have mixed arrangements, so check the record’s technology and notes before interpreting a hydro category as entirely new energy from natural river flow.
Why can hydropower generation change between years?
Available water and operational decisions affect production. A reservoir also may be managed for needs beyond electricity, including flood control and environmental requirements. Constant installed capacity therefore does not imply constant annual generation. Compare several years before treating a wet or dry year as a permanent trend.
Sources: US Department of Energy: Types of hydropower plants
Does hydropower have environmental impacts?
Yes. Dams and associated operations can change water conditions, sediment movement and aquatic habitats. Reservoirs can also release greenhouse gases, with outcomes differing by site. A renewable classification does not replace an environmental assessment, and one project’s impacts should not be assigned to every hydropower facility.
Sources: EIA: Hydropower and the environment
Can a hydropower station guarantee electricity during a drought?
A nameplate capacity figure does not demonstrate drought-period energy availability. Assessing that requires information about water, storage, operating constraints and the period of interest. When an atlas record lacks those inputs, present it as installed capability; do not equate its MW rating with assured continuous supply.
Atlas context: Data coverage and methodology
How can I compare hydro plants without double counting?
Check whether records identify individual generating units, separate powerhouses or a whole complex. A reservoir name can be shared by several structures, and similar names do not prove duplication. Keep source identifiers and location notes when examining a river cascade, then confirm the reporting boundary before adding capacities.
Atlas context: Data coverage and methodology
Textbook references
The science on this page follows these standard engineering textbooks. See the full bibliography.
- Hydropower Engineering HandbookReservoir, run-of-river and pumped-storage schemes.