Heiliger See (English: Holy Lake) is a lake within the city limits of Potsdam, Brandenburg, Germany, located northeast of the city center and bordering the historic park known as the New Garden.

There are numerous unofficial bathing and relaxation points along the banks [1], specifically nudist sunbathers cluster along the north shore in several small meadows formed by gaps in the trees [2][3].

It has a connection to Lake Jungfernsee and thus to the Havel River’s extensive network of waterways via the Hasengraben, a short canal where the water is kept dammed up to maintain a high water level for the lake.

In summertime the depths can be virtually without oxygen, causing dead ecological zones.

[4] Despite this, divers have encountered certain fishes whilst diving, such as pike, eels, perch, and the common rudd, in the period of time between May and September.