How to start cold water swimming

You've heard that cold water swimming does wonders for your mental health and wellbeing, and you're impatient to get started. So, how do you take your first dip in cold water?

Winter swimming has been growing in popularity for a few years, but this year's pandemic has accelerated that growth. It's no coincidence that the pandemic has also magnified mental health struggles because cold water immersion is one of the best ways to improve wellbeing and supports treatment for mental health conditions like anxiety and depression, which is why more people are trying it out. So, having heard about the benefits of cold water dips, how do you get started?


What is cold?

To begin with, it helps to qualify cold water and look at how our bodies react to it. The human body temperature hovers around the 37-degree centigrade mark and it isn't very good at adapting to extreme temperatures. In fact, it's the human mind that adapts; we put on clothes, we light fires, we invented central heating and we avoid getting into hot lava or ice-cold water.


In fact, our bodies only have a couple of physical tricks to combat the cold, like goose pimples and shivering. We're so sensitive to the cold, that our ability to control our breathing is compromised in water cooler than 25C, which is why swimming pools are heated to 25C to 31C. As the mercury drops, it becomes more difficult to control your breathing and hold your breath, and the rate at which your core body temperature drops increases. By the time our core temperature reaches 35C, we are officially hypothermic.


Below 15C is when the water temperature becomes very dangerous. In fact, cold water shock, which is the biggest cause of death in open water, is at its most extreme between 10C and 15C. To the unacclimatised, it causes total loss of control over your breathing, gasping and hyperventilation, and the rate at which your core temperature drops becomes rapid, and continues to drop for 30-40 minutes after you get out of the water (afterdrop) increasing the chances of becoming hypothermic.


Below 5C is extremely cold. Below 4.4C, the water becomes painful -- the numbness in your hands and feet can be excruciating at this temperature. Again, you can expect to lose control of your breathing and your afterdrop will be even deeper.


How do people do it?

If it's so dangerous, how do people swim in water when the temperature is in single figures? The key is becoming acclimatised. This is when you get your body used to cold water by slowly, gently and progressively dipping in colder and colder water. The idea is that you start when the water is 15C or warmer and then you dip twice a week as the temperature drops.


The process of acclimatising does two things: firstly, your body adapts (or maladapts: you actually train yourself to lose some of the fight-or-flight lifesaving reactions to cold water) to the decreasing temperature; and secondly, you get to know how your body reacts to the cold at a safer temperature where there's more room for manoeuvre, learning the signs or 'tells' that it's time to get out and learning how to recover. This is really important because it means you can deal with the afterdrop without getting hypothermic.


How do I start?

If you're cold water curious the best thing you can do is wait until the water temperature is 15C or above and then start swimming at least once or twice a week. To begin with, keep your dips short and expect your breathing to feel much more difficult than in the pool, and your limbs heavier like you're swimming through treacle. Plan to be in the water for up to one minute per degree (skins) or two minutes per degree (wetsuit) for your first six swims, then you can start to see if you can extend the time you spend in the water. After a late spring, summer and early autumn of swimming outdoors, you'll be ready to embark on your first winter.

Open water temperatures UK

As the temperatures drop so should the amount of time you spend in the water. Be extra careful at around 10C to 14C because after a summer of swimming, these temperatures won't feel too bad. But remember that your cold water shock will be most extreme at these temperatures and that your rate of cooling will be more rapid giving you a deeper afterdrop. This is when you start really needing to plan for winter swimming. This means always wearing a swim hat (bobble hat is fine if you swim heads up breaststroke), never jumping or diving in, not staying in too long, and taking warming up very seriously.


By now, you should have a few months' of outdoor swimming under your belt, and you'll know your body. Your body will have also had time to adapt to cold water, and your cold water shock response will probably be less pronounced than it was when you first got into 15C water, which might surprise you. Follow cold water safety advice, keep dipping regularly and you will be set to swim through winter.


It's January... can I start now?

Living is about balancing risk and benefits, and having read about why it's best to start when the water temperature is 15C or above, the decision is yours about whether or not to start cold water swimming when the temperature is in single figures. I advise against it; I think that it is too risky and it's not very pleasant.


If you do decide to take your first chilly dip in January, it is imperative that you:

  • dip, don't swim, for no longer than two minutes

  • wear a swim hat or bobble hat

  • get dressed immediately afterwards in lots of warm layers

  • eat something and have a warm drink

  • take somebody with you to look after you

To the unacclimatised, these temperatures cause intense cold water shock, that's a sharp rise in your blood pressure plus hyperventilation and gasping. For this reason, you must always enter the water slowly and never jump. The other risk is of post-swim collapse where your blood pressure drops sharply when you get out causing you to faint. In this situation, you should lie down somewhere warm and elevate your legs. A deep afterdrop or hypothermia is another risk, and this is caused by staying in too long and not warming up properly afterwards -- remember that your core temperature will drop for 30-40 minutes after you get out.


The best way to swim outdoors in winter is to start in late spring and keep swimming regularly right through to the following winter.