[4] This triangular lake surrounded with spruce forest is located about 6 km northwest of Železná Ruda under a 300-metre-high cliff on Jezerní hora (1,343 m).

There is a natural outflow through Černý potok, a short stream which is a tributary of the Úhlava River.

The oldest pumped-storage hydroelectric plant in the Czech Republic (built 1929-1930) is located here; the lake serves as its upper reservoir.

Due to proximity of the German border (about 1 km), access to the lake was very limited during the Iron Curtain era.

This was exploited by communist secret services in Operation Neptune (1964) when the Czechoslovak StB in collaboration with the Soviet KGB covertly sank cases containing old captured Nazi SS RSHA documents in the lake and subsequently "accidentally discovered" them there.