Cold Water Swimming

Emily and I are not real cold water swimmers, but we’re exploring that option. We’ve started doing some cold water swims, which for us living in Barcelona, means swimming in 20ºC water this time of the year. Emily recently wrote a post on her initial cold water experiences, and particularly on the sudden drop in energy she felt when we moved to do a 1k swim in a 28ºC pool after doing 2K in 19/20ºC.   We’ve also reached out to the real cold water swimmers out there, and they have been very generous with their insights. These are some of the things we’ve learned.

“Cold” is relative.

In the process of trying to learn more about this subject I have discovered a breed of swimmers who excel in cold water and who have redefined the meaning of cold. For swimmers such as Loneswimmer, I now know that cold water starts at 7.9C, and that at 16ºC British and Irish swimmers “actually feel a bit guilty about swimming in such warm water”. His post introduces a precise (and shocking) open water swimming temperature scale which helps put “cold” in perspective. 


Being able to swim in cold water requires discipline and it’s not something you can rush into.  It involves a gradual process of cold water acclimatization and trying to do too much too soon is not the way to go.  Once you gain a certain level of cold water tolerance, it can be quickly lost if you do not maintain a certain frequency of cold water training.  Cold water acclimatization will improve your tolerance and your ability to swim gradually longer distances.

My suggestion – is little and often. Then extend your range as you find it easier. Build it up gradually and not try to push your body too much too son.  Carl Reynolds, Cold Acclimatization

Getting cold water exposure at least once every two weeks, once every week if possible. Don’t worry about doing more than 30 minutes at temps from 9C to 10 C. At temps about 10C extend your time.  TheGreatCthulhu, Swimmit


When you swim in cold water, the reaction of sprinting to try to warm up seems natural, but is it the right thing to do? I’ve been able better tolerate cold water when I make a conscious attempt to swim at a relaxed pace instead of going all out.   You don’t want to overdo the relaxed swimming though, as swimming too slow could accelerate the initial signs of hypothermia.  Sled_Driver recommends to start fast and then settle on a paced rhythm.  Our conclusion is that each swimmer needs to test how their bodies and minds react to cold water under various paces and combinations, but chances are that a relaxed slightly exerted pace will do the trick.

Start relaxed to stretch out the muscles, then up your pace if you feel the need to. For myself, relaxed all through is better. It’s partly a physical thing – cold water contracts muscles, so I take it easy to start, but feel no need to be speedy. Carl Reynolds, Cold Acclimatization

Swimming slow in cold water is highly dangerous, far more dangerous than swimming fast, because you are still losing heat from moving, but not generating enough heat internally. Swimming slow means quicker onset hypothermia. TheGreatCthulhu, Swimmit

You want to get yourself red hot as soon as possible to start generating heat….and THEN maybe do some of those stretches after you’ve acclimated to the best of your ability. Swimming always requires a warm-up period that is a combination of stretching and getting the blood going. With extreme cold water your priority is getting your blood going and wits about you first. You can switch gears after the initial. Sled_Driver, Swimmit 

Hard core

Don’t take swimming in cold water lightly.  You can improve your cold water tolerance and even enjoy the feeling of turning into an ice cube, but cold water swimmers need to be highly aware of the dangers associated with this activity. Hypothermia is inevitable and cold water swimmers need to learn to recognize the different signs and stages of hypothermia so they can get out before it’s too late. Any activity that requires you to detect signs of your body starting to turn off qualifies as hard core.

In Understanding Hypothermia in Swimmers,  Loneswimmer shows that at water temperatures below 15ºC (see chart below), hypothermia is inevitable.  It’s just a question of time. Loneswimmer also describes in his post the signs of hypothermia progression that swimmers need to be aware of.

Survival Time and Water Temperature

Yes I am cold, but I’m not dying or going to die anytime soon.” I have found that I relax into the cold. I know I’m in trouble if I cannot touch my fingertips to my thumb tip. For others there will be a different physical sign. Carl Reynolds, Cold Acclimatization

I think most ‘cold water’ swimming will involve some level of hypothermia. It’s important to know what the signs are, so you can look out for them when swimming and know when you need to get out. Ellethemermaid, MyChallenge

You offset the possibility of hypothermia through acclimatisationCold shuts off peripheral blood flow. But movement means thermogenesis, generating heat through burning ATP. But …at the very same time, you are moving heat into your periphery, and dissipating it faster. It’s a race that no-one can win. All you can do is train. TheGreatCthulhu, Swimmit

As the water temperature drops in Barcelona from the current 17-19ºC to around 14ºC in March (still not worthy for British and Irish swimmers), we’ll continue to relate our experiences with colder waters swims.

Categories: Cold Water, Training


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