I live in Northern Europe, and next to our community is a large lake that people like to swim in at all times of year. During the middle of summer the water can

I live in Northern Europe, and next to our community is a large lake that people like to swim in at all times of year. During the middle of summer the water can get up to maybe 25c, and during winter there is a 10cm+ layer of ice and it's full of fishermen. At that time people cut a hole in the ice where you can take a plunge or go for a quick swim. I haven't tried it myself but people who do it regularly say that if you do it every day - say starting in the summer and continuing until winter - you don't notice the temperature dropping so much. We also have the same rumours about health benefits, but I'm not sure what the science says. I'd guess if there are any, it's more from being somewhat active (locals usually walk to the lake) than the temperature. We also like to roll in the snow after sauna. Our life expectancy isn't any better than warmer climates.