Cold water shock is a danger for anyone entering water 15°C or below so if you're swimming in cold water here's what to do

Cold water swimming has become extremely popular, and with the right preparation and cold water swimming gear, there’s no reason why you shouldn’t enjoy it.

However, wild swimming in cool water can also be dangerous. The RNLI is reminding cold water swimmers to be aware of the risks, after saving the lives of five wild swimmers, and rescuing a further 12 last winter.

Is cold water swimming dangerous?

Cold water shock is a danger for anyone entering water that is 15°C or below. Swim failure and hypothermia can also pose a risk at this time of the year when the average sea temperature in the UK and Ireland is just 6 to 10°C.


Reduce the risk of cold water shock by wearing wetsuits and take a tow float for visibility

Wearing a wetsuit, gloves, boots and hat, and getting changed quickly afterwards can help reduce the risks of cold water swimming, but it pays to understand what’s happening to your body.

What is cold water shock?

Cold water shock is your body’s reaction to sudden immersion in cold water. When you enter cold water the body goes through a range of cardio-respiratory responses.

The first is a gasp of breath – something we’re all familiar with when we jump in a swimming pool or the sea (note ‘cold water’ needn’t be icy cold. Even on a hot day you can suffer cold water shock if the temperature is not what your body’s expecting).

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This is followed by rapid breathing (hyperventilation). Don’t panic – the initial effects of cold water will pass in less than a minute. The key is not to swim straight away but simply float whilst you get used to it. If you have a tow float, now is the time to hold on to it.

Your blood pressure increases as your body tries to keep your blood warm by moving it towards the middle of your body, and away from the extremities. Hands and feet will feel the coldest.

When the initial shock passes, you can start your swim. However, if you’re new to cold water swimming, be aware of your body, and if you feel your strength failing, and are not able to recover your breath, get out of the water.

What is swim failure?

Swim failure is the point at which your strength, endurance and co-ordination fail as a result of the blood moving to your body’s core, and your muscles cooling. You can’t swim anymore. Unless you’re holding onto a float, or wearing a buoyancy aid, you could drown.

Is hypothermia a risk for cold water swimmers?

Unless you’re doing a long swim, hypothermia isn’t likely to affect you in the water. Even in really cold water it takes at least half an hour for you to become hypothermic.

However, it’s when you get out that it becomes a more likely risk. At first you might not notice the cold, but it’s important to warm up as fast as you can.

Get out of your swimsuit or wetsuit quickly, and wear warm clothing, hats and gloves. A changing robe helps to keep you warm whilst getting changed. Have a hot drink ready too.

Big increase in cold water swimmers

Liam Fayle-Parr from the RNLI Water Safety Team says: ‘We’ve seen a big increase in the number of people taking up dipping and open water swimming, and it’s amazing so many people are feeling the benefits of a new activity.

‘However for many, this is their first experience of the sea in the colder winter months, so we’re asking everyone to be aware of risks before they enter the water, know how to keep themselves and others safe, and to Respect the Water.’

5 wild swimmers rescued

Last winter, volunteers from Hayling Island RNLI saved two cold water swimmers who were spotted clinging to a buoy, and while off the Sunderland coast, a group of swimmers called 999 after losing sight of one of their friends who was then saved by the RNLI.

In Sligo Bay, Ireland, four swimmers found themselves in trouble in large swells. One person was recovered by the RNLI, one made it ashore independently and two others were airlifted to safety.

When is the sea coldest?

‘With the sea temperatures still dropping and reaching their coldest around March, the effects of cold water, combined with weather conditions and any personal health issues should be taken seriously before venturing in,’ says Liam.

‘If it’s your first time in open water, we’d recommend you speak to your GP first, particularly for those with cardiac or underlying health conditions’.

How to swim safely in cold water

There are plenty of things you can do to minimise risk when swimming in winter. Avoid swimming alone, but if you still wish to go, find a spot popular with dog walkers, for example, or a nearby cafe. Look for others in the water you can swim close to.

Research the water – are there are rocks, currents or rip tides you should be aware of? If there’s a lifeguard hut (though, not likely in winter) ask them, or another swimmer for advice.

Think about the depth, and plan a swim parallel to the shore where you can touch the ground, rather than out to sea or the middle of a lake. 

If there’s a red flag flying, don’t enter the water. Note, this might not just be because of sea conditions, but something else such as sewage overspill. If there is a lifeguard hut you can enquire there.

Wear the right cold water swimming kit

As well as keeping you warm, a full-length winter wetsuit will increase your buoyancy, and wetsuit gloves, boots and a swimming cap will help keep your head and extremities warm. Ear-plugs also protect you from the cold.

A tow float will help make you visible to others. You can also keep a mobile phone and whistle inside this, or a waterproof pouch, in case you need to call for help.

When you get out, ensure you have warm clothing to hand and a means of getting home quickly to warm up if you can’t get warm outside.

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Call for help

The most important thing to remember is if you are in any doubt, stay out of the water and if you or anyone else gets into trouble in or on the water,  call 999 or 112 and ask for the Coastguard.

In November, Newquay RNLI launched to a swimmer in difficulty who was quickly spotted thanks to her bright swim cap and airlifted to safety. And in Scotland, a cold water swimmer got into difficulty when finding herself in deep water but managed to hold onto her tow float before Kinghorn RNLI plucked her from the sea after receiving multiple 999 calls.

The RNLI’s top tips for cold water swimmers

  • Be prepared – Check the weather forecast, including tide information and wave height. Take plenty of warm clothes for before and after your dip, along with a hot drink for when you come out of the water. Take a mobile phone in a waterproof pouch. Wearing a wetsuit will help increase your buoyancy and reduce the chances of suffering cold water shock
  • Never swim alone – Always go with a buddy, if possible, to a familiar spot and tell someone when you plan to be back
  • Acclimatise slowly – Never jump straight in as this can lead to cold water shock, walk in slowly and wait until your breathing is under control before swimming 
  • Be seen – Wear a brightly coloured swim cap and consider using a tow float
  • Stay in your depth – Know your limits including how long to stay in the water and swim parallel to the shore
  • Float to live – If you get into trouble lean back in the water, extending your arms and legs, and resisting the urge to thrash around to gain control of your breathing
  • Call 999 or 112 and ask for the Coastguard – if you get into difficulty or see someone else in trouble call for help immediately
  • If in doubt, stay out – there is always another day to go for a swim