Oh yeah, that is hardcore. The coldest I ever really swam in was 20°C, when I was a kid. It was an unheated outdoor pool that was so lovely that we just ignored the cold. I've been in colder water in Canada but it was more like jump in, scream, paddle around a bit an jump back out.

Our municipal outdoor pools are all having problems this season because they're solar-powered which sounds like a good idea but of course in a summer like this one it doesn't work. The temperatures hover around 20°C. That really sorts the hardcore swimmers from most everybody else.