Rummelsburger See, Bay section of Spree-Oder Waterway in Friedrichshain-Kreuzberg, Germany.

Rummelsburger See is a bay section of the Spree-Oder Waterway in Friedrichshain-Kreuzberg that forms a central water feature in eastern Berlin. The shoreline is lined with walking paths and open areas where people can stop to rest or watch the water.

Settlers on the Stralau peninsula originally called this water body Spree See before it eventually gained its present name. The waterway developed as Berlin expanded its role as a trading and industrial center.

The bay's name comes from the innkeeper Rummel, whose name spread from the Rummelsburg settlement to the water by the 1770s. The Liebesinsel island was called Entenwerder until the late 19th century. The northeastern shore held the Städtisches Flußbad Lichtenberg, a river bath heated by waste heat from the Klingenberg power station in the 1920s; it closed in the 1950s and its structures were removed.

Paths around the lake allow for walking, cycling, and relaxing time by the water in any season. Wear sturdy shoes since path conditions vary with the weather and ground surface.

Since 1 June 2024, a special regulation bans unmanned mooring of boats and rafts in the bay, after noise and rubbish from house and party boats had to be cleared at public expense. Boaters must now keep a supervisor on board and may anchor only in side waters or at marked berths.