You’re the adventuresome sort. You’re hiking in the Southern Alps in winter. Unfortunately, you unknowingly cross a small, ice-covered lake. The ice breaks and you find yourself neck-deep in very cold water and no way to get out. What’s going to happen to you?

Ask this question down the pub and you’re invariably going to hear a chorus of “Hypothermia, mate. You fall into cold water you’re gonna die of hypothermia – everyone knows that.”

Well, yes and no.

Cold Shock – The First Minute

Water conducts heat 25 times more efficiently than air, so heat-loss will be far faster in water. Even so, hypothermia still takes about 30 minutes to set in, and between an hour and two hours to kill you. Before this, if death does occur, it will probably result from complications due to something called cold shock.

During the first minute of immersion in very cold water (less than 10 degrees) the body undergoes a massive reflex reaction. This is characterised by an uncontrollable gasping for breath, disorientation, and impaired coordination – all factors which may render a person incapable of swimming effectively and so lead to drowning.

The second potentially deadly effect of cold shock results from the body’s physiological reaction to a sudden drop in external temperature. Upon entering dangerously cold water, blood is pulled away from the skin and shunted it to centre of the body in an effort to maintain core temperature. This rush of cold blood to the heart may cause cardiac arrest.

Ok, say I don’t drown or have a heart attack during this first, critical minute – then what?

The Next Ten Minutes

Your next window is ten minutes long. As your body scrambles to protect its core temperature, it progressively cuts off blood flow to non-essential muscles. After ten minutes of this, your ability to perform the physical actions necessary to save yourself (treading water etc.) declines substantially due to muscle weakness.

Obviously, if you can’t get out of the water during this period you’re in serious trouble – you’re not going to be able to keep your head above water and you’re going to drown.

Yeah, but, mate, I managed to spike the collar of my Swandri to the ice with my knife. My head ain’t going under.


Stage 1

Ok, your extremities will lose more and more strength and you’ll begin to feel numb and mentally foggy. In an attempt to warm itself the body will begin to shiver – this is a good thing, don’t try and stop it. Your body temperature, usually around 37 degrees, will begin falling and once you hit about 35 degrees you’ll have entered stage 1 hypothermia.

Stage 2

Still no rescue party racing through the snow to save you? Stage 2 hypothermia here you come. Want to make sure? Try touching your thumb with your little finger – if you can’t do it, it means your muscles are failing.

Your temperature will have dropped by as much as 4 degrees, your shivering will have become violent, you’ll be suffering mental confusion, you’re movements will be slow and laboured and you may have difficulty seeing.

Stage 3

Stay there any longer and you better start praying for the sudden arrival of the Westpac chopper. You’re in stage 3 hypothermia – body temperature 32 degrees, losing consciousness, shivering becoming sporadic and eventually stopping, heart rate severely lowered.

Don’t Give Up

But don’t give up, depending on your clothing, fatness (this is probably the only situation you’re going to find yourself in where fatter is better), and physical and mental conditioning, getting to this point could take an hour or more, and you’ve still got a way to go yet!

Death from hypothermia occurs when your body temperature reaches 28-29 degrees and your heart stops beating. It takes about two hours for your core to cool to this point. So, as long as your head stays above water and you don’t drown, you could still be rescued and successfully revived.

You’ve Got Time, But Not a Whole Lot

If you’re planning on tramping across an ice-covered lake this winter you can take heart from the fact that, if you fall in and survive that first minute of cold shock, you aren’t going to die immediately. But don’t wait too long to haul yourself out of the water – you’ve got about ten good minutes. After that you’re heading for hypothermia and you’ve got about as much time as it takes the Warriors to lose at Eden Park before you have to kiss the wife and kids goodbye.

Learn more about the body’s reaction to immersion in cold water here.

Cold Shock and Hypothermia – What Happens to the Body in Very Cold Water, 5.0 out of 5 based on 1 rating

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  1. Linda says:

    Thank you so much for this video and study/information. Our friends just lost their son at Coal Lake, Alberta. His body was recovered today(one week after they were reported missing), along with his friend’s body. They too were not wearing their life jackets and their boat overturned in frigid waters. This video should be on the news everywhere when people are recovered from drowning. I had no idea that it took 30 minutes for hypothermia to set it, but now I understand that you can die within 5-10 minutes of falling in without a life jacket in frigid waters. Point very well made!! Thank-you.

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