Cold Water Shock: What Swimmers Need to Know

Why UK Waters Take Your Breath Away

Around the UK coast, sea temperatures sit somewhere between about 6°C and 9°C in late winter and rarely climb past 17°C or 18°C at the height of summer. Rivers, reservoirs, lakes and many outdoor pools are colder still, especially where water drains off high ground. Cold water shock can begin at anything below roughly 15°C, which means that for most of the year, most of our open water is cold enough to trigger it.

The reassuring part is that cold water shock is predictable, it passes, and understanding what it does gives you a great deal of control over it. Swimmers who know what to expect in the first minute handle it far better than those who don't.

What Happens in the First Minute

Cold water shock is a set of automatic bodily responses, not a sign of weakness, poor fitness or inexperience. It happens to everyone.

Within seconds of immersion, cold receptors in your skin set off a gasp reflex. You may take an involuntary sharp breath, and if your head is under water at that moment, you can inhale water instead of air. This is the single biggest danger.

Next comes hyperventilation. Your breathing rate can multiply several times over, and it feels as though you cannot get enough air. At the same time, blood vessels near the skin narrow sharply, pushing heart rate and blood pressure up. For most healthy people this is uncomfortable rather than dangerous, but it does place extra strain on the heart. If you have a heart condition, uncontrolled high blood pressure, or you are pregnant, speak to your GP before taking up cold water swimming.

After a minute or two, the gasping eases and your breathing begins to settle. Then comes cold incapacitation: hands, arms and legs lose strength and coordination. In genuinely cold water this can arrive within five to ten minutes, which is why attempting a long winter swim is a poor idea even for strong pool swimmers.

Enter Slowly and Breathe Through It

Almost all of the risk in cold water shock can be managed by controlling your entry. The golden rule is simple: get in slowly, and let your body adjust before you ask it to do anything.

• Wade in step by step. Never dive or jump in, however tempting on a hot day.
• Splash cold water on your face, neck and wrists before you go further. This helps trigger the dive reflex and softens the gasp.
• Stop at waist depth and stay there for 30 to 60 seconds. Let the shock arrive while your feet are still on the bottom.
• Breathe out through pursed lips, long and slow. Extending your exhale is the quickest way to calm the hyperventilation.
• Move on to shoulders, then chest, then swim. Give each stage a moment.
• Keep your first swims short — three to five minutes is plenty when the water is below 12°C.

Never swim alone in open water. Tell someone where you are going and when you expect to be back, use a brightly coloured tow float and hat, and check the tide, wind and current before you get in.

If It Catches You Out: Float First

If you fall in unexpectedly, or the gasp arrives before you are ready for it, the priority is not to swim. It is to float.

Roll onto your back, let your ears go under the surface, spread your arms and legs like a starfish, lift your chin and scull gently with your hands. Float first, then breathe, then think, then act. Almost everyone floats. Thrashing and clawing at the water burns energy, increases panic and cools you faster.

Count slowly to sixty. For most people the gasp reflex eases within that time and the breathing settles. Shout for help only when you have breath to spare, using short, single calls. If you are with others, keep talking to each other — it keeps breathing steady and shows everyone is still alert.

Once your breathing is under control, make a decision. If shallow water or a safe exit is close, swim on your front at an easy pace, keeping your head clear of the water where you can. People get into serious trouble because they gasp and inhale water, or because they strike out in a panic towards a shore that is further away than it looks.

Getting Out and Warming Up Properly

Core temperature often continues to fall for twenty to thirty minutes after you leave the water. This is called afterdrop, and it is why you can feel colder on the beach than you did in the water.

• Get out before you feel you need to. Leaving it until you are shivering hard is leaving it too late.
• Get out of wet kit and into dry layers, dressing from the top down to protect your core first. A hat makes an enormous difference.
• Warm up gradually. A hot shower or bath straight away can cause a sudden drop in blood pressure and make you feel faint. A warm drink and a gentle walk are better.
• Avoid alcohol. It widens blood vessels near the skin and speeds up heat loss.
• Do not drive until the shivering has stopped and you feel fully clear-headed.

Violent, uncontrollable shivering, slurred speech, clumsy hands or an odd feeling of warmth are signs of hypothermia. Call 999, get the person sheltered and dry, and keep them still and warm.

Small Habits That Keep You Safe All Year

Cold water swimming is genuinely wonderful once you are acclimatised, and acclimatisation is built slowly rather than bravely. Swim with a buddy. Start in summer and keep going through autumn so the temperature drops gradually around you, shortening your swims as it does.

Check the tide, currents and water quality before every dip, and give rivers and estuaries a miss for a day or two after heavy rain, when flows are strong and pollution washes in. Choose an exit point before you enter, and if you can, get in and out at the same place.

Treat cold water with respect rather than fear. Enter slowly, breathe out long, know how to float, and get warm afterwards. Do that, and you will enjoy our coasts and rivers safely for years to come.