Spotted these two just standing in the sea... no attempt at swimming... I had to ask them what they were doing and the answer is they were recovering from rugby training... Cold water immersion is a training regimen usually following a period of intense exercise in which a substantial part of a human body is immersed in a bath of ice or ice-water for a limited duration... well it's summer in the UK so the sea will be ice cold :)
The things you learn! Don't think I'd be too into ice immersion - can see its use, though. Wonder if you can even feel your lower limbs after a few minutes!