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Acclimation To Cold Water

International Ice Swimming Association 1

Competing in an International Ice Swimming Race

Experiments have shown that people can reduce the cold-shock response by 50% in as few as 5 two-minute immersions in cold water 59F (15C). Moreover, most of the habituation remains for up to a year. Brief cold showers have a similar but less marked effect. 

- Golden and Tipton, Essentials of Sea Survival

Acclimation (acclimatization) is a process by which your body gradually adapts itself to cold water through repeated exposure. Through acclimation, it’s possible to greatly reduce or eliminate cold shock.

Be Realistic

Few recreational boaters are acclimated to cold water, and acclimation is not a valid reason to skip wearing thermal protection. If you decide to go this route, you should be experienced at cold, open-water swimming and certain that you can function for the entire time that you might be in the water - for example, if your boat happens to blow away.

Different Strokes
Most people unfamiliar with cold water find 70F (21C) to be quite cold. On the other hand, a competitive open-water swimmer who is used to swimming in 55F (13C) water will probably think that 70F (21C) doesn’t feel very cold at all. Even more extreme are the International Ice Swimming Association competitors who swim in water as cold as 28F (-2.2C).  What’s important to your own safety is how you personally respond to cold water.

International Ice Swimming Association 1

Acclimation and body fat can make a significant difference in how someone responds to cold water.  Repeated exposure to even cool water increases the layer of fat directly under the skin surface (subcutaneous fat).

Body fat is an excellent insulator. Seals, whales, and other warm-blooded aquatic mammals have a lot of this insulating fat - called blubber - which enables them to keep warm while swimming in cold oceans.

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Well-Insulated From The Cold

Because fat provides insulation from the cold, it can delay incapacitation and hypothermia and also improve physical stamina in the water.

You can often see this body fat difference by comparing the physical appearance of Olympic swimmers and runners. Swimmers tend to have more subcutaneous fat and a sleeker, streamlined look. Runners have very little fat and more obvious muscle definition.

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Michael Phelps

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Usain Bolt


Reduce the intensity of cold shock.


Protect you against incapacitation, swimming failure, and hypothermia.

Body Fat

Provide insulation, slow heat loss, delay incapacitation and hypothermia.


Reduce the intensity of cold shock.

What About Your Hands?

It's reasonable to think that there might be a way to acclimate your hands to cold water

A Very Remarkable Swim

An excellent example of how body fat can prolong cold water survival is the remarkable case of Icelandic fisherman Gudlaugur Fridthorsson. On a cold night in March, 1984, Fridthorsson was working on a 75 foot (23 meter) commercial fishing vessel when its nets snagged on the ocean bottom and caused the vessel to capsize three miles off the rugged coast of Iceland's Heimaey Island.

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How in the world did he do it?

In a word, he was obese. At 6'4' and 275 lbs, he had a chart-busting BMI in excess of 30. His physique was similar to a seal’s.

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Acclimation and Cold Water Swimming
Acclimation and Cold Water Swimming
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A Painful Process In Freezing Water

Three Challenges

Without the protection of a wetsuit, cold water swimmers face three challenges: cold shock, incapacitation, and hypothermia. Cold shock is an involuntary response that cannot be consciously controlled. In people unaccustomed to cold water exposure, it reaches maximum intensity between 50-60F (10-15C), and involves huge gasps and a complete loss of breathing control, which results in swimming failure. Incapacitation is a progressive reduction of the control you have over your arms, legs, hands and feet. It also results in swimming failure, but the process is more gradual than with cold shock.


Easy Does It

The process of gradually increasing one's cold tolerance is called acclimation (also acclimatization).  Our advice to those who want to increase cold tolerance is "easy does it" on the front end. Your body is very adaptable, and a process of gradual water entry and a brief exposure of several minutes begins to produce results after several exposures.


Gradually increase the length of time that you spend in the water. You don't need to swim at first, in fact, it's safer if you initially go in only waist or chest deep and squat down so that the water covers your skin. Although it appears to be less effective, you can also acclimate by taking cold baths or showers.

Protect Your Ears

It's wise to use a neoprene swimming cap or ear plugs to prevent cold water from entering your ear canals because repeated exposure can result in the development of bony growths called external auditory exostoses, also known as Surfer's Ear.

First Sign of Progress

Your first sign that the process of acclimation is working will be more control over your breathing.

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Very Well Acclimated

Although you'll easily notice the reduction in cold shock responses as your acclimation increases, judging the length of time that you can safely continue swimming will take a lot more practice. That's particularly true if you don't have much body fat.


Be Cautious

The danger here is that the nerves and muscles in your arms and legs will cool to the point where they're too weak to work properly. You don't want to be in the water, trying to swim, when that happens. Also, when the nerves and tendons get cold, your fingers can splay (spread apart) which makes them less effective for swimming.

My father almost drowned while competing in a one-mile ocean swim in the spring. It was his second swim of the day, and towards the end his body just stopped obeying commands. He told me later that he was completely lucid, was watching his friends cheering him just 50 yards away on the beach, and realized he was going to drown. He couldn’t even wave an arm. Someone wading just a little inshore of him realized something was amiss, and went and got him before he went under.

- Andy Taylor on the Tsunami Rangers Blog 

Transition from Swimming To Standing

Another important point about swimming is that water provides a lot of buoyancy. When you reach shore and transition from swimming to standing, your cold muscles may not have enough strength to support you. It takes time to develop cold tolerance and also judgment about the length of time that you can safely swim without thermal protection in cold water.

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Mario Vittone, a very fit and determined former US Coast Guard rescue swimmer struggles to stand after completing a short unprotected swim in 45F (7C) water.

See our Water Temperature Safety Guide for more information.

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