Swimming in the Rhine river in Basel (Switzerland) has been possible for a long time and is even officially sanctioned by the city https://www.basel.com/en/activities-excursions/swimming-rhin...
Going down the Aare river from Thun/Uttigen to Bern is a hugely popular activity to do in summer, but every year a few people drown. Even so, I'd recommend it.
https://madeinbern.com/en/stories/along-the-aare-river-2#:~:...).
https://www.visitcopenhagen.com/copenhagen/activities/baths-...
It might have a slight upper hand in cleanliness with being directly connected to the sea.
To any tourists visiting Aus, please only ever swim where locals swim and only between the flags if on the coast
Not open water, but salt, and an absolutely gorgeous location.
I guess it's open water unlike the Seine, but it did surprise me, I felt like I was sat in quite an industrial area when a couple walked past in swimming costumes and towels.
On the other side, Arve coming down from France is muddied right at the source by Mont blanc range, which is mostly granite. You can see the exact spot where specific stream comes into play, very gray, and it doesn't get much better afterwards.
Its enough to get big river like Rhone dirty all the way to Mediterranean sea. Also, after Jonction Rhone becomes pretty cold to just swim in even in warmest summer days. But yes many tkae it down during summer on inflatables, including us.
while the thames can be swam upriver of Putney Bridge, there are conditions as the Thames is a busy river. but there are other spots in London where one can do wild swimming.
for example:
london royal docks https://loveopenwater.co.uk/swimming-london-royal-docks/
canary wharf: https://canarywharf.com/whats-on/open-water-swimming/
the famous ponds in hampstead heath: https://www.cityoflondon.gov.uk/things-to-do/green-spaces/ha...
the famous hyde park lido: https://www.royalparks.org.uk/parks/hyde-park/things-to-see-...
There are lots of canals and rivers all across The Netherlands and people are swimming in them more and more. When I used to live in Utrecht the idea of swimming in the Oudegracht was disgusting. But I was visiting last month and saw people doing it. I still wouldn't swim in that canal.
We had a rubble beach and the river only was 1m deep for half its width.
Was pretty nice. The water was colder than in the lakes and it came with a natural counter-current system, so you could swim in-place.