Dolní nádrž Dlouhé Stráně, Lower reservoir of a pumped-storage plant in Hrubý Jeseník, Loučná nad Desnou, Czech Republic

The Lower Reservoir of Dlouhé Stráně is a reservoir that forms part of an underground pumped-storage power plant located in the Jeseník Mountains and collects water from the Divoká Desná river. It works in tandem with an upper reservoir on the mountaintop above, with water flowing through subterranean tunnels to turbines housed in vast underground caverns carved from rock.

The lower reservoir was built as part of the Dlouhé stráně pumped-storage plant, whose construction ran from 1978 to 1996 with a halt in the early 1980s and a resumption in 1985. The plant pumps water between this reservoir at 825 m and an upper reservoir on the summit, generating power at times of peak demand.

The dam is 306 m long and 58 m high, holding a triangular water surface at 825 m above sea level; the Divoká Desná flows through it. Two underground feeders, 1.5 km long and 3.6 m in diameter, link it with the upper reservoir. Salmon and carp live in the reservoir.

The entire power plant is hidden beneath the earth, shielding it from harsh mountain weather and minimizing impact on the surrounding landscape. This underground arrangement was an innovative solution of its time and made the facility an example of how large-scale infrastructure can coexist with the natural environment of the Jeseníks.