Spandau: Großer Rohrpfuhl

The two, in the extreme north of the Spandauer forest lying, partially Verlandeten waters (large and small Rohrpfuhl) occupy altogether an area of ​​30.5 hectares. Similar to the devil's break today's Rohrpfuhle originated from a lake, which was increasingly silted up as a result of the construction of a drainage ditch and the Spandau waterworks. Since the 1980s, this process has been successfully stopped by an irrigation system, which - unlike the devil's breach - does not consist of water pipes but of water ditches that were formerly used for drainage purposes. The forest path, which had been piled up in the mid-1930s through the silted Great Reed Pipe, was restored in 1996 to protect the habitats. Since then, the Rohrpfuhle are accessible only from the outside.
Source and more info: Wikipedia