The construction of the aqueduct was caused by the massive floods that often plagued the areas at the foot of the Krkonose or Giant Mountains. The most devastating occurred on July 29, 1897, hitting her two-thirds of Bohemia, parts of Moravia and Silesia, and parts of Austria and Germany. Rising waters in the Elbe and Upa rivers have damaged many villages in the Giant Mountains and killed 102 people.
In response to this disaster, the Austro-Hungarian central government decided to regulate waterways in Czech lands and began construction of two canyon dams above the Elbe River. One of the dams was built at He Krausovy Budy under Špindlerůvmlýn and another at Těšnov above his Dvůr Králové.
Also known as the Těšnovská Dam or the Bílá Třemešné Dam, construction of the Forest Kingdom Reservoir began in 1910, based on a project led by Josef Prikka, at a cost of 4.7 million Austrian crowns. The dam he completed in 1920 became the largest reservoir in Czechoslovakia at the time.
The reservoir is located 50 km on the Elbe. It covers an area of about 532 square kilometers and includes many tributaries in addition to the Elbe River. In an emergency, the reservoir can hold up to 9.2 million cubic meters of water.
The dam, including the power station, has been on the permanent National Heritage List since 1964. In July 2010 it was also declared a national cultural monument of the Czech Republic.
https://english.radio.cz/forest-kingdom-reservoir-8758328 Forest Kingdom Reservoir | Radio Prague International