outdoor pools (Canton of Zurich)
outdoor pools (other cantons)
6 chf to enter.
It's near the zoo. :-)
If you want to take exercise, Rialto probably is perfectly fine for you.
If you want to have fun or want to relax or maybe want to go there with kids, then Laguna would be the perfect choice. It's in germany, very close to the border to Basel.
Hmm I'm not a big fan of Rialto as whenever I've been (admittedly only on a weekday evening which I am sure is peak time) there have been far too many people and they also don't readily move out of the way of oncoming swimmers to make the swimming experience more enjoyable (I'm not fast enough to go in the lanes!). I'd recommend the pool in Allschwil as it is wider than Rialto though saying that I have also only ever been there on a Sunday and it's usually not so busy so you can swim in relative peace and have some space to yourself.
http://www.badi-info.ch/bs/allschwil.html
Best pool I've found is the one just over the border on St Louis/Village Neuf border (La piscine couverte). It is a bit of a trek to get there when relying on public transport but if you have the time and/or a bike it would be much quicker. I've only ever been right on opening time on a Saturday morning but really enjoyed the few times I've been. Think on weekends it fills up quite quickly. There are two pools here (Bassin Sportif and Bassin de Nage - the latter is often used for swimming clubs). I may try here on a weekday evening soon and see how it is, otherwise Allschwil on a weekend, when I can manage to go!
http://www.cc-3frontieres.fr/piscine-village-neuf.html
opening times: http://www.cc-3frontieres.fr/FR/173
If you don't have a car, you may want to try out the Rialto, it is just decent.