Lake Walchen is one of the deepest and largest alpine lakes in Germany, with a maximum depth of 192.3 metres. Its genesis is the reason why is became so deep: Walchensee fills a tectonic valley which is part of the Bayerischen Synkline or Bavarian syncline.
Some sources state that the Nazi's dropped some of the gold they took from the Reichsbank and dropped it in deep lakes in this nieghbourhood. The Walchensee would be a good choice because it's depth.
Kochel am See