The polar bear dip is a winter tradition with some Canadians. They jump into freezing water. Frostbite is a very common occurence, so I can't say I fully understand the DESIRE.
But I do repect these people.
The strip's general idea stems from the fact some "spring" breaks in Canada are held in February. When the temperature is stil -18 deg Celsius, and the snow is still falling. This was the case with my university, Dalhousie (Halifax, Nova Scotia).
Of course, if you had money, you could always head South where the temperatures there are also in the double digits, but this time on the + side of the thermometer.