“What temperature of water is too cold to swim in?” Redux

Annual mean sea surface temperature from the W...

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The post entitled “what temperature of water is too cold to swim in?“,  was for over a year the site’s most popular.

This is a slightly updated version (main changes in italics), specifically the list of factors affecting ability.

This post was courtesy of searches on the site as a few variations of this question had cropped up.

I guess I could divide my thoughts on lowest possible water temperature in which to swim into three camps.

  • 1 degree WARMER than it is now
  • What it is now
  • 1 degree COLDER than it is now

Substitute any temperature reading into the above sentences…because cold is fairly subjective, (up to a certain point). I used to be in the first category, moved to the second, and am now definitely in the third. (All this means is I’ve (now) swam in 4 C. which makes me know it’s possible for me to swim in 2 C. It’s a moving target, last time those figures were higher).

I’ve pointed out before some of the things that affect your ability to deal with cold. Here’s the updated comprehensive list.

  • What weight are you?
  • What shape are you?
  • What shape are you in? (Fitness)
  • How did you sleep last night?
  • Are you tired just before you swim?
  • Have you drank alcohol in the last 24 hours?
  • Have you eaten (properly) today?
  • Are you well or ill?
  • Or have you been ill recently?
  • Have you swam in similar temperatures before?
  • If so, for how long?
  • If so, how often?
  • If so, how many times?
  • If so, how long ago?
  • Does Open Water scare you (just be honest with yourself)?
  • How well do you know the location?
  • Are you cold before you swim?
  • Is it sunny or cloudy or raining?
  • What’s the air temperature?
  • What’s the wind direction?
  • What’s the wind speed?
  • Is it choppy or calm?
  • What have the conditions been like for the last few days and weeks? And what are the prevailing conditions for your location?
  • How motivated are you?

So, as you can see, there are lots of variations just with these parameters. Some, like illness, are less likely but you really need to be aware of your own experience and take it incrementally.

One can’t reasonably expect to go from pool swimming to doing an hour in 7C / 45 F without a wetsuit, based on desire to swim alone. Granted, this isn’t likely to occur, but I’m trying to illustrate a point.
Ability to handle COLD is again a matter of a few factors being more important than others (all other things like alcohol, food, illness, sleep being equal): namely, experience and weight.

People with plenty of experience of cold can swim in very cold water. I can swim for 20 minutes in 5 C / 40 F water, because I’ve gotten used to it. But I certainly don’t recommend it and I won’t claim it’s fun. I’ve kind of changed my opinion on the fun aspect.  And the bigger and heavier you are the more you can handle with less training. Fat is an insulator. Just having plenty of fat alone makes cold easier to deal with. But fat does not lessen the pain of the initial shock for example.
The effect of wind is very significant. Any Northerly wind in Ireland is inevitably cold as may easterlies. Heat will be stripped from your body faster while swimming and while trying to get dressed. Any wind will generally cool you faster. And there is no thinking your way out of it out of wind. A similar effect is whether there is sunshine or not. Swimming the Guillamenes on a flat day which is calm, with no wind, warm air and sunny can lead to big difference than a choppy windy overcast day. even though the water may be no warmer, you can feel much more comfortable, due to the lack of wind combined with direct sunshine and calm water. I’ve said previously, wind is the swimmer’s enemy.

I can also tell you, without any embellishment, that my reactions to various temperatures are entirely different now than they were two years ago. I wrote a chart for myself of my reactions and estimated comfortable swim times at decreasing temperatures below 12 Celsius. That chart is now entirely useless as a current indicator, but is interesting to me as an measurement of how far my ability to handle cold has changed.

Some evidence says regular immersion in water temperatures of less than 10 Celsius is very beneficial for health, in a few different areas; improved respiration and circulation, lessened chances of infection and heart attack. However once the time goes over 10 minutes some of those benefits tend to reverse, especially hypertension and cardiac arrhythmia.

Update: Here’s my own scale of water temperatures and the possibilities.

If you are arriving here from USMS, board.ie or any of various pointers here, please note the Cold section on the top menu and you’ll find other more extensive writing on the subject.


17 thoughts on ““What temperature of water is too cold to swim in?” Redux

  1. this is a late post, it’s November 10, 2016. In past years I’ve swam sporadically in the Willamette river near our house, (it’s about 11 Celsius this time of year). As late as November 22, and usually the earliest I swim there is during Good Friday weekend in late March. But this year, I’m aiming to do it every day; today was my 15th day, for about an hour, a couple of days more, and a couple of days less, because I got there close to dark, and wasn’t comfortable swimming and then biking home in the dark. I am better able to handle the cold this year, and it is FUCKING exhilarating!!! and yes, the euphoria and rush is all there—but I am better able to handle the After-effects, what Donal, I think you call the “After-drop” with all its shakes, can’t hold a cup of hot liquid—can’t type, (I tried to type an angry email soon after a cold water swim once and couldn’t for the life of me, just kept shaking, it was something terrible that had happened to my daughter I was responding to) but this year, not only is it the first year I’m trying to swim through the winter—but I think my circulation is better too, I did a boot-camp amount of high -intensity dancing last year—sometimes 3 to four hours a day, heart pumping, sweat—and even though cold is the opposite—I think it’s improved my circulation, I don’t get the shakes now. I do put on a heavy sweatjacket when I ride home afterwards, and cap, and as the weather gets nastier, I’ll have to don warmer wear home—but when I get home, I’m not shaking like someone scared out of the bejesus by a haunting—instead I immediately put on dry clothes—which I know most swimmers do immediately afterwards (but doesn’t work on a bike, in a public place), and then I dance for a short time—often to French singers in the Caribbean ha ha, like Willy Williams or Maitre Gims, or Luyanna, etc., and then I am totally warmed up. I start out with socks, and three shirt layers, and dance until I am in my tanktop and warm once again. Just saying, if you have the time, it’s a good strategy to continue your body moving, and warm up at the same time, and switching from cold to hot is supposed to be good. Would be interested in other people’s experiences as well regarding this, and if my good circulation theory is all bogus ha ha. Whatever it is, KEEP SWIMMING IN COLD WATER! it’s fucking fantastic! Really enjoy this blog!! Donal. Makes me feel not TOTALLY ALONE!!! there are no other cold water swimmers in my neck of the woods. 🙂


    • I’m a cold water swimmer from Crosslake, MN. I swim without any wetsuit until about late Oct to early Nov. I also have swam for 20 min on Nov 22 in about 40 degree water. Any longer and that might have been dangerous.


    • Right before I read your post, oceanusspiritus, I went for my first ow “swim” in the Willamette today! Thank you so much for all the information, LoneSwimmer! It was 5°C(41°F) & I wore a wet suit, neoprene cap & gloves. The worst part was trying to peel off the wet wetsuit & swimsuit to get dry clothes on… Very motivational to try to work up (down?) to swimsuit alone. Maybe tomorrow I’ll try it with the sleeveless wetsuit?


  2. Pingback: What Is Cold Water Swimming? Part 1 – What Governs Ocean Temperature? | LoneSwimmer

  3. Trying to swim in lake much warmer than Ireland here in North Cal. I love swimming in cold water but don’t know how long before I need to worry about hypothermia. Generally swim 1hr in 54 or higher. Great for my severe depression.


    • I don’t know what I’d do without swimming either. At 54f, an hour or two should be fine. There’s a (good) dichotomy in that the more you swim the better you will be able to monitor any deterioration while at the same time the better able you will be to deal with it. Mild hypothermia, (~ 1 degree C lowered core temperature) is pretty normal though. I’ve got posts on the various stages of hypo on the site if they are helpful. Best of luck from a fellow sufferer.


  4. Pingback: Swimming in Cold Water | Myrtleville Swimmers

  5. Will be in Killarney 5/25-26 25-26015. The ice in Pa. Will just be melting and I wont have a lot of time in the lake yet. Would like to swim while I’m there. Any suggestions appreciated. Thanks Pat Lyons


    • Hi Pat, your dates are confusing, but if it’s May of 2015, the Killarney lakes should be quite warm, 14C at least and possibly higher. All you have to worry about is the lamprey eels in the lower lake…


  6. Pingback: Open water wetsuit | just Trying to Swim

  7. I swam all last winter for the first time ever, and it was quite an experience. I’m not sure if I’ll repeat it, the biggest factor for me is it takes about 1000m to start to feel more limber, but then the body heat diminishes rapidly from that point onwards. I was expecting temperatures of 8-10 C but someone told me it was as low as 4 C this year with the extra cold northerly air. It depends if this winter is more normal or another especially cold one.

    Probably the biggest factor for me is getting into several layers of clothes as quickly as possible. It’s strange that I can be sitting around doing nothing and feel cold and then go for a swim and a flush of heat comes on soon after and feel less cold for the rest of the day, hope it’s a sign of good circulation.


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