Ice swimming is a legit sport in these countries, practiced by both young people and old. I'm assuming Bear Grylls has the appropriate training.
You don't seem to have a grasp of the situation.
BG passes his antics off as appropriate in a SURVIVAL situation. Intentionally making yourself hypothermic?
We're not talking about a controlled sport where you go home and drink beer at night.
Just like one of his first episodes where he crossed the river (with a life jacket, of course). Dipshit jumps right into the rapids. An ill prepared person trying to cross a rapid without a lifejacket is likely to drown, or be injured by the rocks. The smarter course of action is to take some time and work your way downstream and find a pool to cross. Take a couple logs and find something to strap them together with, strip, put your clothes on the log, and swim naked, thus keeping your clothes dry. Get out, air dry, build a fire and warm up if its real cold, dress into your dry clothes. Live.
Doesn't make for good tv, though.