 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.This came to light in "The Deception Game", published in 1972 by Ladislav Bittmann.