What is "tajchy"

Tajchy (singular: tajch, from German teich) are artificial water reservoirs in the Štiavnica Mountains, in central Slovakia. Most of them were built in order to provide energy for the silver mines of Banská Štiavnica in the 18th century. At their height, tajchy comprised a sophisticated system of 60 reservoirs, connected to each other by more than 100 km of channels and underground tunnels. 24 artificial lakes still exist and serve recreational purposes. Because of their historical value, tajchy were proclaimed by the UNESCO to be a World Heritage Site on December 11, 1993, together with the town of Banská Štiavnica and technical historical monuments in its surroundings.