Mellensee Lock

The lake, which is up to nine meters deep, is part of the chain of lakes Wolziger See - Großer Wünsdorfer See - Kleiner Wünsdorfer See - Mellensee, which flows from the Mellensee via the Notte Canal into the Dahme. The chain of lakes lies on the southwestern edge of the Wünsdorfer Platte in the Töpchiner Talung, a glacial channel from the Weichselian Ice Age. The Great Wünsdorfer See drains into the Mellensee via the Wünsdorf Canal, which is around three kilometers long.
Source: Wikipedia

The lock connects the Notte Canal with the Mellensee and is one of three locks in the canal. The canal was completed in 1864 and enabled the economic boom in the region. Numerous brickworks were founded that used the new transport route. Today the canal is mainly used by leisure boats. Several hiking trails lead along the former towpath. The “Dahme-Notte” Water and Soil Association is responsible for the lock.

Source: reiseland-brandenburg.de/poi/flaeming/schleusen/schleuse-mellensee/?no_cache=1

There is also a small rail car to help carry kayaks here.