Yea, Alte and Neu Donau are safe but Donau and Kanal... I see people do it with a balloon strapped to their waist for visibility to boats, but I wouldn't do it.

Yea, Alte and Neu Donau are safe but Donau and Kanal... I see people do it with a balloon strapped to their waist for visibility to boats, but I wouldn't do it. Those pontoon ferry boats travel over 30 km/h on the Kanal.