Last updated 2026-10-20
Winter water quality in Berlin lakes and the Spree
What our winters at the lakes and on the Spree have taught us about water quality, and why nobody should ever go into the Rummelsburger Bucht.
Lakes in winter
Most of the lakes we use are summer swimming lakes, and in winter the biological load in the water usually drops, because it is too cold for many of the bacteria and algae that make the Spree such a poor place to swim in July. This is our own experience together with the seasonal pattern that hydrologists describe, and we have no lab results for every single Saturday.
The Spree after rain
After heavy rain, overflow from the combined sewers can enter the Spree around Osthafen, although Alt-Stralau is usually still in better condition than the stretches further downstream. The Rummelsburger Bucht is heavily contaminated with arsenic and should never be used for dipping. For reliable information, please read the pages of the Senate and of Flussbad Berlin rather than relying on our Telegram group.