https://www.youtube.com/watch?v=DkY-9oc3KGs
This is a bit weird, I found it by accident on YouTube it's a ladies swim in the River Medway starting a couple of miles from where I live.
I wouldn't dare swim in the river here, too many have drowned, I stopped a suicide on the bridge a few years ago.
There used to be a floating swimming pool in the river at Rochester, it might be what you can see in the background.