A lot of people also jump off into the river near the park behind the Swiss National Museum (near the HB) and then float and swim down to the spot mentioned above. That spot is located right where the Limmat and Sihl rivers split (or so I think that's what it does right there).
I'm pretty sure you can just go in there, without having to pay.
Have fun!
Further up the river is Werdinsel, which has a small but nice area for river swimming. There is a cafe nearby, and more shade than at Oberer Letten. There is a small children's wading area if you have kids, too. All free.
Grab a group of friends, and just float down the Limmat.
There are train stations next to the Limmat at Dietikon, and Kilwangen (Kanton Argau) that will take you straight back to Zurich.
Failing this, for Swimming, I still prefer the Unterletten at the Dammweg walk bridge (tramstop near the Viadukt markets).
It has a grill in the water you can put your feet against and use the current to just keep your head out of the water.
change rooms and showers. all quiet.
.... did I mention a short stop at the 'Mousetrap pub' at the Viadukt on your way home?
Don't be surprised if people look at you like you are crazy. We started doing this in 2006 and it did not seem to be very common.
fduvall
https://www.google.ch/maps/preview#!...!1m1!1e4&fid=0
I take along a "Schwimmsack" ( http://www.slrg.ch/de/nw/sektionen/b...bestellen.html or http://www.transa.ch/de/produkte/beu..._062827-005010 ) to put my shoes, clothes, wallet and mobile phone in.
Are you freaking serious?
There are many indeed, but some quite quiet are around Hardeggsteg Bridge:
https://maps.google.com/maps/ms?ie=U...031f68bb69bebf
I hope you enjoy it in a sunny day!
C