depoint...depends on several variables. But Justin is right....all riders need to learn the symptoms of hypothermia. I just wrote an article on it for our wakeboard club (Canyon Lake) and it should be posted soon. But it also depends on wind speed, air temp, water temp, insulation(fat) content of person, and just how a person can tolerate cold temperatures. But it doesn't matter how tough you are, if you stay in cold water too long for a certain amount of time your core temp IS going to drop and you will be at risk of hypothermia. Just be smart and educate yourself on hypothermia. The formula most use is 100 but my formula is 140---70 water temp and 70 air temp
(I'm a whimp!!)