Until the late 19th century the Danube River, or Donau Kanal, was unregulated and formed a 5-mile (8 km) wide wetland which regularly flooded nearby villages around Vienna. In 1870 the river was dammed and a new river channel formed for shipping. The mighty river continued to flood periodically and after 1972 a new flood-control project was started. This resulted in the creation of the Danube Island and Danube Canal or Little Danube, which runs past the old town. Both are now popular as picnic areas. In June, the annual Danube Island Festival attracts over 3 million visitors.
In summer, the Viennese flock to the Old Danube to swim, sail, row, paddleboat and even surf! Okay, so that's in a wave pool but there are still three surf and sail schools, plus beaches including a nudist area. Something for everyone.
There are various boat tours you can take along the Danube, into the Danube Valley, up to Bratislava in Slovakia or downstream to Budapest in Hungary. Metro line U1 goes to the river, stops: Alte Donau (Old Danube) or Danube Island.