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Assume you want to do some cold water swimming, i.e. anything under 14 Centigrade (57F) water, for more than say 10 minutes (so, expressly, not a Polar Bear "dip and scoot").

What's the safest approach?

  • Wade/jump in quickly and get it over with.

  • Go in very gradually, legs first, then groin (ugh), torso and then finally your head. I easily take 2 to 3 minutes myself, hating every second of it.

(In both cases lets assume you are starting out in shallow water but will proceed to swim later on)

Does it matter much? Any studies done?

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    This is 57 degrees F, which is cold -- about the temperature of high Sierra lakes in the summer. The one time I went into water that cold, I was chasing a cooling champagne bottle that had broken free from it moorings and was being swept away in the Tuolumne River., so I had no time to ponder. No ill effects at all. If I had to do it in cold blood, so to speak, I would go in to my hips, and then splash water on my tum until my tum got sort of acclimated, then quickly dunk all the way in. Note that it is easier if you have a layer of cloth over your tum.
    – ab2
    Jul 25, 2023 at 1:10
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    General ballpark of Vancouver ocean temperature this time of year, maybe a little lower than what you actually see on a shallow beach: Minimum water temperature (6.5°C) in Vancouver it happens in January, maximum (14.5°C) in July. I would expect possibly much worse from a mountain lake. Jul 25, 2023 at 6:34
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    I've often wondered if the slow way is more torturous for tall folk, or do we have the same amount of feely receptors as everyone else and as they're distributed evenly it's no different? Jul 25, 2023 at 21:36
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    Based on nothing but frequent experience; jump in quickly and get it over with. Disclaimer: I have heard (and do believe) that this may pose a risk to those with a weaker heart.
    – user25462
    Jul 25, 2023 at 23:35
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    @ChrisH 6'3" here and I know the feels 😆. Maybe it's a question for a physiology stack? Do humans tend to have a constant ratio of hot/cold feely receptors per body, or more a constant ratio per surface area. Assume a constant BMI. Jul 26, 2023 at 21:13

6 Answers 6

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The worry with going in fast is cold water shock (RNLI, the main UK lifeboats and beach lifeguards). The cardiovascular effects are a particular concern if you get in fast and immediately put in a lot of effort, but the main issue is that even the mildest forms lead to gasping for breath, which can be uncontrollable, and lead to drowning if your face is in the water.

So if you go in quickly, you're increasing your risk. This can be mitigated by ensuring that you don't go right in quickly, but only if the water depth is perfect.

The UK Outdoor Swimming Society's safety tips include "Enter the water slowly, be wary [of] the gasp reflex"

Based on that, and what works for me, I wade in fairly quickly, splashing my chest and upper back once it's easy, and squatting into the water once any gasping has stopped. It may start again. This is in the context of somewhere beach-like and needs to be adapted for steeper entry.

Note that acclimatisation can help a lot, but it takes a lot to be acclimatised, like open water swimming several times a week. Even regular cold showers can help, but in my experience only go a small way.

Some indicative numbers, noting that individual responses vary a lot: I'm an occasional outdoor swimmer so never get truly acclimatised. In summer (15--16°C or 60°F) getting in quicker - but still cautiously - works for me compared to colder times of year (10-11°C or 50°F is the coldest I've done without a wetsuit, at 5°C/41°F even with a wetsuit the gasping took long enough to stop that my hands were already going numb).

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    BTW neoprene shorts are really good, a game-changer at around 11°C for me. I had some wetsuit leggings that I never wore, and cut them down to something far more useful. You can also wear a thermal rash vest when you get in, and take it off once your skin has cooled if you don't like swimming in it and you've got somewhere to put it
    – Chris H
    Jul 25, 2023 at 8:46
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    What I found most informative here was the cardiac risk associated with exertion and cold shock. I knew of the cold water shock, but I assumed the risks were limited to the initial submersion and drowning because of reflexive water inhalation. All big risks when you fall overboard or jump off a pier. What I didn't realize is that even shallow water doesn't make it risk free. To quote from your first link: Cold water shock can therefore cause heart attacks, even in the relatively young and healthy.. Jul 25, 2023 at 21:12
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    Cardiologists may also tell us that sudden cold shocks may stress existing (and possibly as-yet undiagnosed) cardiovascular conditions in the most surprising and inconvenient of ways.
    – uhoh
    Jul 25, 2023 at 22:21
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    @uhoh that risk is certainly to be taken seriously. I didn't concentrate on it because my sources weren't clear on how beneficial a slow entry is in managing it. The gasping aspect on the other hand is familiar and definitely benefits from a cautious approach
    – Chris H
    Jul 26, 2023 at 5:40
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    The rise and fall of a swell/surf is pretty effective for that "splashing before immersing" part that people suggest. No avoiding each incoming wave. I take another step or two forward between each wave. Jumping doesn't work well. Before I know it I'm all wet and off the bottom.
    – John Mee
    Jul 28, 2023 at 4:58
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I'm an all-year round open water swimmer in Scotland, so highs of around 18°C in summer, lows of around 1.5°C in winter (requiring breaking ice to get in) and for most of us, the usual technique is to walk in up to around waist height, then splash cold water on the face and neck - which helps the body prepare - and then swim.

Any new swimmers are encouraged to use a wetsuit, and strictly limit their immersion time, until they are used to the way the cold affects their body. We also encourage them to swim with an experienced group until they are full comfortable.

If the body of water is very deep, or the conditions are rough, or if there is vessel traffic, we always take a bright flotation device. It helps boat captains see us, but also can be held onto in case of cramp, excessive tidal rip etc.

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  • I'd die in about as many seconds as we have fingers. Sep 20, 2023 at 8:13
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You don't have to jump in the water to get accustomed to the temperature quickly. Splashing yourself with water has essentially the same effect: once you're wet, (re-)entering the water for a swim is not as bad as when you're dry and warm. On the other hand, spilling water over yourself avoids the risk of drowning.

Going in up to the waistline and then sitting down is another (at least seemingly) safe way to do deal with the cold quickly: if you gasp for air, your head will still be above water.

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A fourteen year old boy in our neighbourhood drowned from cold shock when he jumped into a swimming pool last winter. Don't do this. It may be happen very very seldomly, but it does happen.

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Took someone waterskiing in January, with a wetsuit on. She fell off, and head went under the water. Stopped breathing immediately - I think it's a bodily safety function. So, more care needed with immersing the face (or head) is needed too. Maybe going in, but ensuring head stays out as long as possible helps. Good news - pulled back in the boat, she started breathing again, after a (anxious) minute.

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I did a lot of cold water winter swimming in the Navy (sans wetsuit, with SEALs who wore them). I didn't do a slow walk, but just went in from the shore at a normal pace. In a few cases, did a racing dive from a boat. But I generally found that it was best to not do the total jumpin, nor the slow walk, but just a normal pace immersion. I was in good shape and in my 20s. But not some superstar. A strong swimmer and used to ocean cold water swimming. It's not that bad once your head gets numb. ;-)

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    While you survived, I think this goes counter the advice of official bodies as well as as experienced and well known members here. Better admit this is limited personal experience and not official advice. Although someone who trained with SEALs will be not your average person.
    – Willeke
    Jul 26, 2023 at 18:23
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    The other thing to consider is that the military have reasons to prioritize training for quick entry, for perfectly valid tactical reasons. Reasons that do not apply to most civilians. Jul 26, 2023 at 19:59

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