Swim safely in cold water

A brutal cold snap and the water temperature has fallen like lemmings off a cliff. It's well and truly winter swimming season, and, serious face now, it's time to reflect on safety.

Chilly dipping

The health benefits of cold water swimming are numerous, for our bodies and our minds. But it's not without its risks. Whether you've been winter swimming for years, or you are new to it, considering the risks and taking precautions isn't an option. This isn't a joy-killer, quite the opposite; do it safely, and winter swimming is one of the most joyful activities on earth.

How can we survive cold water?

Freezing cold water can be fatal. And yet, it's possible to swim in water that's below zero degrees centigrade. How?

To start with, it helps to understand the physiology of cold water immersion. But before we start, it's worth flagging up this small but significant disclaimer: there is a lot of contradictory information out there, and the way our bodies respond to being in cold water is still not fully understood.

One thing we do know is that we have a profound cold water shock response. This is what happens in the first 90-120 seconds of being in cold water. Frigid water on our skin is probably the most profound stimuli we'll experience, so the reaction is dramatic too.

Hearts, lungs and blood pressure

First of all, our capillaries and blood vessels close. That means our hearts have to work in overdrive to pump the blood around the body, and that increases blood pressure. There's no downplaying that strain on the heart: it's what can cause a heart attack. At the same time, our respiratory system responds by gasping in-breaths; clearly that's not the moment to have your head under the water, and actually it's people jumping in and then gasping under the water that causes the most drowning accidents. Our breathing rate can increase by tenfold.

Once those first crucial minutes are over, we settle into the water, attenuating the stress response and getting used. This is when you might start to feel numbness or aching in your fingers and toes. Why? It's called 'peripheral vasoconstriction' to give it its proper name. This is when the blood vessels in the skin are reduced in size, limiting blood flow to the surface of the skin so that more of the heat in the blood supply is moved the deep tissues of the body. That means the skin, hands and feet get very cold, but our core stays insulated.


The next response is shivering. Our bodies stimulate the shivering response to increase our core body temperature, and this can happen in the water or 10-15 minutes after we get out. Because shivering is an involuntary contraction of the muscles it makes it hard to swim. But as you get better adapted to cold water, you shiver less. This makes it easier to swim: but be warned, it comes at the expense of greater deep body cooling. That's why it's very important to listen to your body and get out before you get too cold.

The danger zone

As we continue to cool, we slowly lose power, our arms and legs becoming slow and heavy. This is cold incapacitation, and it can cause us to lose coordination as well as strength. Swimmers can then start to become confused and disorientated, and most dangerous of all, lose powers of rational thinking.

Beyond this start, there's hypothermia. But this is actually pretty rare among cold water unless you stay in cold water for too long.

The afterdrop

Once you get out of the water, the physical reaction doesn't stop. Most cold water swimmers are familiar with the afterdrop, a reaction that happens once you're dressed. This is where the cooler blood from your skin mixes with the warmer blood at your core contributing to an overall drop in your core temperature. This can trigger a serious attack of the shivers!

The urge to pee

When you get into the water, you can get overcome with the urge to pee. This is because the body's response to an increase in blood pressure is to get rid of liquid elsewhere. The easier liquid to lose is urine, and this is called cold immersion diuresis.

But even experienced cold water swimmers can struggle to relax their muscles enough to empty the bladder completely. There's something else going on too. Cold diuresis means that more liquid processed by the kidneys goes to the bladder instead of being absorbed. This is because the cold suppresses the production our anti-diuretic hormone that stops you peeing, which means you need to pee more.

The inconvenient side-effect is that when we leave the water and our muscles relax but our core is still cold, that urge to pee can become uncontrollable and leave us briefly incontinent.

Staying safe

While there are risks from swimming in cold water, so long as you're sensible and prepared, the benefits for your physical and mental health far outweigh the risks. Here are some guidelines to follow:

  • Arrive warm: make sure you're toasty before you get in.

  • Don't swim alone: make sure your swim buddy knows your name and if you have any medical conditions that might be relevant in the water or in an emergency.

  • Check with your doctor: if you have hypertension, heart condition or have ever hand cold-induced asthma.

  • Get ready to warm up after your swim before you get in: have lots of warm layers, a hat, gloves, a warm drink and something to eat and put them where you can easily get them when you get out.

  • Get in carefully: take it steady as you get in and don't put your face in until the cold water shock stage has passed.

  • Wear the right gear: a hat and ear plugs are a must, and many winter swimmers add neoprene. If you don't want to go full wetsuit, you may find gloves and socks just as beneficial.

  • Listen to your body: You'll feel cold, then ok, then you'll start to feel colder. This is the point to get out.

  • Don't stay in too long: it's not clever!

  • Off with the wet, on with the dry: take off your wet swimmers and put on your warm clothes, socks, shoes, gloves and hat as quickly as you can.

  • Drink and eat: a warm drink (not hot) and something sweet do wonders.

  • Find warmth: hot water bottles, hand warmers, radiators, car heaters, heated seats are all favoured by cold water swimmers.

  • Don't shower: hot showers cause your blood vessels to open up too fast which can give you chilblains and sends cold blood to your core too fast deepening your after drop.

  • Go for a stroll: if you feel up to it, gentle exercise will help raise your core temperature.

Get used

Take it slowly, dip for a shorter time than you think you should and gradually increase the time. Swim at least once a week, if possible two to three times. Respect the cold water and feel the icy bite and feel the high afterwards.