Fláje Reservoir, Water reservoir in Český Jiřetín, Czech Republic

The Fláje Reservoir is a valley reservoir behind a pillar dam on the Fláje Stream in Český Jiřetín, Ústí nad Labem Region. The dam is 56 m high and 416 m long, with a hollow construction; the water surface covers 153 ha. A concrete wall with a low railing borders the water on the left, and dense trees line the far shore.

Construction of the Fláje Reservoir began in 1951 to manage water flow and protect the surrounding mountain region from flooding. The project represented a major infrastructure effort in the post-World War II development of Czechoslovakia.

The dam is a cultural monument of the Czech Republic, listed for its hollow pillar construction, chosen because cement was scarce during the 1951–1964 build. The village of Fláje (Fleyh) was flooded to create the reservoir, and the hamlets of Vilejšov, Oldříš, Mackov and Pastviny were abandoned. In 2013 Česká pošta issued a stamp for the dam's 50th anniversary, designed by Adolf Absolon and engraved by Martin Srb.

The dam is reached from Litvínov via road II/271 (17.5 km) or from Hrob via road II/382 (18 km). A first-degree protective water zone bans entry to the banks around the whole reservoir, so viewing is from the dam and its surroundings. The outflow feeds the Rauschenbach reservoir below.

The dam is the only concrete pillar hollow structure of its kind in the Czech Republic, making it a technical rarity in the country's water infrastructure. This unusual construction method holds particular interest for those curious about engineering solutions.