One of the last historical uses of the Spree Canal was as a river pool not far from the Berlin City Palace; however, that bathing area was closed in 1925 for hygienic reasons.
The most severe pollution occurs when Berlin's combined sewage system overflows, which happens roughly 20 to 30 times per year during periods of heavy rain.
One case in point: as it makes its way towards downtown Berlin, the Spree River runs through the Müggelsee, a lake located near the city but just before the sewage overflow sites and whose water quality is generally high.
In fact, when a certain number of days have passed after the most recent overflow of the sewer system in inner-city Berlin, the overall water quality of the Spree Canal returns to a level that is actually quite good – it can even have a visibility depth of up to 2.5 metres.
The actual swimming area would lie between the Schleusenbrücke and the Monbijoubrücke, i.e. in the section of the Spree Canal between the upcoming Humboldt Forum and the Bode Museum.
At two points here – at the Lustgarten and at the Humboldt Forum – descending stairs along the riverbank would give visitors direct access to the Spree, whether to swim or just enjoy the view.
At the northern tip of Museum Island, a new end-weir would separate the clean-water area of the canal from the regular main flow of the Spree River.
The largest technical challenge facing the Flussbad comes in the form of the raw-sewage overflow pumped into the Spree Canal by the combined sewage system during heavy rain.
In that study, both the water purification system proposed by the Flussbad as well as the use of the Spree Canal as a so-called "river pool" were deemed feasible by independent scientists.
In November 2014, the association received €4 million funding from the Berlin and German governments as part of the "National Urban Development Projects" programme.
The international reception of the project has been overwhelmingly positive; the Flussbad was described as emblematic of Berlin as a modern, future-oriented capital by Michael Kimmelman in the New York Times[11] and Max Kutner in Newsweek.
[12] The fact that the Spree Canal is officially listed as a Federal Waterway (Bundeswasserstraße) has caused some speculation that the Flussbad might come into conflict with existing laws.