@Wen When I lived in Balqhuidder I used to swim in Loch Voil, but I found it too physically painful to go into very cold water. I didn't have much insulation on my body at that time of my life, and the pain in my feet in particular was agonizing.
My cousin used to do a collective New Year swim in the Tay. His wife wrote on his swimming cap, "Do Not Resuscitate!"