Cold-water paddlers are at particular risk of capsizing and going into the freezing drink (especially in the Northeast, where frigid ocean and lake temperatures lag far behind the warming weather of spring), but it can happen in other unexpected ways. A tumble off a boat dock, a fall through thin ice...all it takes is one freak incident to put you in a potentially life-threatening situation.
1 Minute: The Cold Shock Response
When you hit freezing-cold water, the first thing you experience is known as the "cold shock response." You involuntarily gasp for breath and begin to hyperventilate. This increased rate of breathing puts you at greater risk for drowning, especially if you panic. The key is to remain as calm as possible and focus first on getting your breathing under controlbefore attempting to rescue yourself. The cold shock response lasts for about one minute.
10 Minutes: Cold Incapacitation
Once you have your breathing under control, you now have approximately 10 minutes before you lose effective use of your hands, arms, and legs. This is your window of opportunity to get out of the water under your own power. Once you become incapacitated, you lose the ability to swim and will drown if you are not wearing a life jacket. (Yet another reason why paddlers should always wear a life jacket.)
1 Hour: Hypothermia
If you are unable to extricate yourself in the first 10 minutes, your only hope is for others to come to your aid. Fortunately, you have more time than you might think. Contrary to popular belief, it takes at least 30 minutes for hypothermia to set in, even if you're submerged in ice-cold water, and generally at least an hour before you lose consciousness. (Lean and thin individuals succumb quickest; overweight individuals with a high percentage of body fat can last several hours.) Focus on keeping your airway clear and alerting others to your dire situation.
For more, check out Dr. Giesbriecht's Cold Water Boot Camp, which features some great videos of cold-water immersion and more in-depth information about what happens to the human body in the minutes (and hours) following an icy plunge.