Heiligensee, Glacial lake in Reinickendorf, Berlin, Germany

Heiligensee is a small natural lake in the Reinickendorf borough of Berlin. It sits among trees and low vegetation, with no large buildings along its shores.

Since the early 20th century the lake has belonged to the Voormann family of Berlin-Frohnau, who sold their other Heiligensee plots during the inflation but kept the water. Dermatologist Dr. Maximilian Voormann protected the biotope; after his death in 1982 it passed to his sons Max, Michael and Klaus. Motorboats were banned, trees planted on the banks, and the lake has been under landscape protection since 1969.

The lake has belonged to the Voormann family of Berlin-Frohnau since the early 20th century; dermatologist Dr. Maximilian Voormann protected the biotope, and after his death in 1982 his sons Max, Michael and Klaus kept up the conservation work. Motorboats are banned and trees were planted on the banks, so beavers settled and the reeds stayed intact. The lake has been under landscape protection since 1969.

The lake connects to the Havel under a road bridge, where a wooden platform gives a view over the water. A lido (Freibad) stands at Sandhauser Straße 132–140. Motorboats are banned, so the surface stays free for rowing boats and swimmers.

Heiligensee is classified as a hypereutrophic lake, meaning the water is so rich in nutrients that algae can form thick mats on the surface during warmer months. This same nutrient richness supports a wide range of birds and insects that make the lake worth visiting for nature watchers.