Kamencové jezero is a lake in the Chomutov District. It is artificial in that it came into being due to 18th century mining.
Wikipedia https://en.wikipedia.org/wiki/Kamencové_jezero
Official Website http://www.kamencovejezero.cz/
Address 43001, Czech Republic
Coordinates 50°28'20.244" N 13°25'30.734" E