I saw a TV segment a couple of years ago, and I think it was from Austria although I'm not sure. Somewhere in Europe anyway. The city canal was during a short period in summer time, a really fast current. This due to melted water from the mountains nearby. Tourists and locals jumped into the canal, and let themselves travel for several kilometers in the fast waters. It looked amazingly fun! But I can't remember where it is. Could you please help me?