[rsync]

This exists already in Zurich. Sort of.

There is a river (a very clean river, of course) that flows through Zurich, and there is a 200 foot or so length of the river that is buoyed/strung off to form a decent sized "pool".

You go downstream, jump in, and swim upstream. You're swimming in the actual river, just inside a marked off area with a nice deck on one side. It's really quite well done.

Here it is:

http://www.zuerich.com/en/visit/sport/lower-letten-river-poo...

[SeoxyS]

In Bern, there's a "pool" I used to love going to. It's got normal pools, but there's also the opportunity to jump into the river, where the currents will easily carry you half a mile in no time.

http://www.bern.com/en/activities/adventure-fun/river-swim/m...

https://www.youtube.com/watch?v=8Dc1vmzjwJE