That "winter dip"/"the long run"

Saw the newspapers today, and apparently, though yesterday here in NY was mild, a number of those who are part of some group that frolics in the ocean in winter, did so yesterday. It would be interesting to know how many may have experienced hypothermia and if not mistaken that requires a low registering thermometer used rectally to check the body's core temperature. I think on the other side of the coin, runners in marathons especially in warm and hot weather are subject to any number of heat related problems and if not mistaken, many are checked in various medical tents set up where it's very likely rectal temperatures are also obtained.