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I will have a trip by the end of this month to a northern country to "escape the heat" where I live in, and I would definitely want to do some swimming at some best beaches there. The expected water temperature would be around 5°C (41°F).

However, as I live in a hot climate, thus "escaping the heat" on the trip), 5°C (41°F) is a big gap from the temperature that I regularly swim in. This year I have swum in water down to 18°C (64°F) well, but the weather in my place hasn't gotten any colder than that this year so I don't know what is my lowest comfortable limit (I am aiming at 15°C (59°F).

In the past I had swum in water down to 13°C (55°F), but at that time I was not serious about cold water swimming. I didn't have any knowledge about hypothermia, and I didn't take my time. I just got out when I felt that my swim form was deteriorating. I think I have encountered the effect of afterdrop once, I no longer know when, how long and what temperature it was at that time as I didn't have knowledge on hypo. At the moment what I knew it was that, I got out when I could no longer hold the form, then ran to the shower room and turned on the hot shower. I still found myself shivering even more vigorously and started fainting, so I turned the shower temperature down to reduce the blood circulation. I only stopped shivering after a relatively long time before I turned the temperature up again. Now I know I was experiencing the effect of afterdrop at that time, and I shouldn't be taking a hot shower at that time, but I don't have the numbers on hand.

So how should I feel when swimming in 5°C (41°F) water, and how should I properly plan my swim and my exit strategy, as the difference to what I am used to is too large for me to imagine?

  • There is plenty of material out there, such as How Cold Water Feels and Tips for Cold Water Swimming. Another page warns against taking a hot shower afterwards. – Weather Vane Apr 1 at 11:38
  • So 7C is roughly the water temperature of a cold tap in the UK, and 15C or below is considered cold. So I'd recommend getting a wetsuit, the RNLI has some information on what is called "cold water shock" and some safety guidelines as well. – Aravona Apr 1 at 12:43
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    5 is lovely for those of us who grew up in the north of Scotland (I would die if I tried to swim in 20 degree water - that's hotter than I could have a bath) but you'll probably hate it. I'd second a wetsuit! – Rory Alsop Apr 1 at 18:37
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5°C (41°F) is very cold water for unacclimatised swimmers, especially if you're used to swimming in 18°C (64°F). You could probably manage a short dip (1 or 2 mins), but I would not plan for longer than than.

A couple of years ago I swam outdoors from May-November in my local lido. The water temperature peaked at ~20°C (~68°F) in August, and by the start of November was 8°C (44°F). In the summer I was swimming up to 5000m, but as the temperature dropped I reduced this down. By the end was I only doing 400m.

The exact perception of the cold depends on a lot of things: size, weight, fat, gender, cold water acclimatisation, etc etc. Personally, while swimming below 10°C (50°F) I would feel a burning sensation from the cold, eventually followed by creeping numbness in the hands and feet. I would get out before feeling cold in my core. About 5-10 minutes after getting out I would sometimes shiver for a few minutes due to afterdrop (when your body temperature drops further after getting out of the water). After about an hour I would start to warm up again.

A few tips if you are still considering it:

  • Take a friend - they can call for help if you get into difficulty and help you warm up/get dressed etc.
  • Just plan for a dip the first time you go in, don't expect to spend more than a couple of minutes in the water.
  • Get in slowly to manage cold shock. Splash water on your face before putting your head under, and expect the mammalian diving reflex.
  • Wear 2x swim hats to provide some extra insulation, and when getting dressed take them off last to keep the heat in
  • Have a hot drink ready for when you get out
  • Pile your clothes in the order you put them on, and make sure everything is the right way round. Trying to turn a jumper inside out with damp numb hands is surprisingly tricky! Take more layers than you think you'll need and a wooly hat.
  • Plan your entry and exit to the water. Don't get into the water before you know how you can get out of it.

I would also check out LoneSwimmer, which is a great cold water swimming blog with lots of advice. Cold water swimming is a great sport, and I definitely would encourage you to get into it, but 5°C (41°F) is probably too cold a starting point.

  • Great answer, only thing I'd add is buy a wetsuit! – Aravona Apr 2 at 7:44
  • @Aravona I have a wetsuit. It does not cover neck, feet... When I touch my neck after swimming 15-20 min in 5°C I don't fell if I'm touching my skin or I'm touching wetsuit. So 5°C is super cold water – user1209304 Apr 8 at 13:21
  • @user1209304 you can get wetsuit boots, gloves, and hoods, and the mm thickness of the wetsuit is also important for warmth. 5C is very cold indeed, especially at depth (I'm a scuba diver) but the insulation provided should still help vs no wetsuit. – Aravona Apr 8 at 14:40
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On a dare with a friend I went into the Saskatchewan River while the river was still running with broken ice, and there were bergybits in the main current. The bet was to stay in 1 minute up to our chins. We both made it, and were cold for half an hour.

In our school program we require that all canoe trips start with a training camp that includes dumping and rescue practice. On two occasions we have done this on lakes that still had pan ice. We do NOT attempt to do a floating rescue under these conditions, but instead get people out of the water into another canoe as fast as possible. Dumping was done dressed for the weather. Clothing helps you to maintain some function for longer.

I've dumped in the Athabasca River in September. The Athabasca is sourced from the Columbia Icefield, and was running high. Temperatures were likely around 5 C. We were in the water for about 25 minutes. We were all at the uncontrolable shivering stage of hypthermia by the time we got out, and getting out of our wet clothing was difficult.

The key with this sort of swimming is to have an out.

  • Stay near shore.
  • Do not venture into currents
  • Do not swim where you will need to grab something to get out.
  • Have a buddy ready and able to rescue you.

With experience you will learn what your reasonable limits are.

Note that one of the symptoms of hypothermia is loss of judgement.

If you want to prolong the time you have in the water, wear a wet suit. It will not keep you warm, but it will keep you less cold. Wearing polypro longjohns under your wet suit will help.

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