I see you live in Baden so perhaps the nearest place to go to would be Reuss Kanu Bremgarten–Gebenstorf. You can take a train to Dietikon and get on another train to Bremgarten. You can check for exact connection on
www.sbb.ch. Here is a link to their website:
http://www.kanuland.ch/en/routen_detail.cfm?id=317137. We did down stream canoeing there last year as part of our outdoor team-building activity and I can highly recommend it. Halfway down the river we stopped for BBQ and canoed all the way to the end after. As far as I remember it wasnt plain white water adventure just a few bearable rapids along the way and mostly the river was calm. You can also try to google for rafting, tubing, kayaking and etc with acronyme CH and might be able to find many more such activities.