[bigbluesax]

The Danube running through Vienna is safe to swim in: https://www.wien.gv.at/forschung/laboratorien/umweltmedizin/... The water quality doesn't protect you from the current or the heavy boat traffic through. So most swimming is done in a disconnected side channel called "Alte Donau".

[insane_dreamer]

There's a nude beach there too (or at least there was 20 years ago)