For what it's worth, please do not go for a dip in the Danube river proper here in Vienna, the currents are too dangerous for bathing and there is no official bathing spot anywhere for this reason. Instead, visit our other waters such as the lakes of the Old Danube or the high-water protection side-arm New Danube.

Yes, good clarification, I personally spend my times at Grillplatz 11 on the Neue Donau side of Donau Insel (Danube Island) .. it has been a wonderful summer and the water is delightful. Very safe and rewarding swim, every time.