Staying warm and safe in cold water

Cold water takes heat from the body much faster than air at the same temperature, so staying safe in it depends on three things: matching your thermal protection to the water temperature, keeping sessions short enough that you do not cool too far, and recognizing the first signs of cooling before they affect your judgment. Cold can cause a sudden emergency at the moment of immersion, as described below. Beyond the first minutes, though, it more often works slowly: it slows your thinking, weakens your grip and makes your breathing harder to control, and those effects can turn an ordinary swim into a problem.

The body's first reaction to sudden immersion in cold water is often a strong gasp followed by fast breathing, known as cold shock. This usually settles within a minute or two, but it is the reason to enter cold water slowly, let your breathing calm down and avoid swimming hard straight away. If you have a heart or circulation condition, or any other medical concern, ask a doctor before a cold-water trip, because cold places extra strain on the heart and blood vessels.

Match thermal protection to the water temperature

A wetsuit insulates mainly through the tiny gas cells in its neoprene, which slow the loss of body heat. Fit matters as much as thickness. A snug suit limits how much cold water flushes through it, while a loose one lets water move in and out with every movement and carries heat away from the skin. Choose thickness for the water you expect. As a rough rule, the colder the water, the thicker the suit, with a hood, gloves and boots added as temperatures fall, and very cold seas may call for a drysuit.

Body size, body fat, air temperature, wind and the length of your stay all change how cold you feel, so ask the local operator what they recommend for the season and the site. Bringing a spare layer costs little, but being too cold in the water is hard to fix once you are shivering.

Check the fit on land before you go in. The suit should feel snug without restricting breathing, the neck and wrists should seal well and the hood should cover the ears. A suit that gapes at the neck or cuffs lets cold water in quickly, and that cold water stays against the skin for the whole session.

Limit how long you stay in

Time in the water is the variable you control most easily. Plan each session around the water temperature and your protection, and treat the first few minutes of a cold swim as a chance to check how you feel rather than the start of a long dive. Shorter sessions with rest in between usually leave you warmer than one long session, especially when the water is cold enough that your hands stop working well. Cold also increases urine production, so you may need to pass water more often, and dehydration can make you feel colder. Drink water between sessions rather than waiting until you are thirsty, and keep a snack and a warm drink in the boat or car.

Recognize the early signs of cooling

Shivering is the body's most visible response to cold, and it is a useful warning. If you shiver and cannot stop, or find that your fingers have become clumsy with a mask strap, a clip or a regulator, it is time to end the swim or dive. Other early signs include numb hands and feet, reduced dexterity, slower thinking and difficulty keeping track of your buddy or the boat.

As cooling continues, people may become confused, speak slowly or slur their words, stumble or lose coordination. In more serious cooling, shivering can stop even though the person still feels cold, which is a sign that needs urgent attention. Any of these signs in yourself or a companion calls for leaving the water promptly, with help if needed. Do not wait for symptoms to get worse before acting, because the person affected is often the last to notice the change.

Warm up gradually after leaving the water

Warming up starts as soon as you leave the water. Take off the wetsuit, dry the body and put on dry layers, starting with the head and torso, since keeping the core warm protects the rest of the body. Move out of the wind and into a warm place such as a heated vehicle or cabin. If the person is fully alert and able to swallow, a warm, non-alcoholic drink can help. Wrapping them in blankets works better than rubbing their skin, and very hot baths or showers should be avoided because rapid rewarming can cause problems.

Boat rides back can feel colder than the swim itself, because wind pulls heat from damp skin. Keep a windproof layer and a dry towel on board, and cover the head as soon as you exit. Avoid alcohol, which widens blood vessels near the skin and can hide the warning signs you need to notice.

Seek urgent medical help if someone who has been in cold water becomes confused, drowsy or unable to walk, if they stop shivering while still feeling cold, or if they do not improve as they warm up. Even milder symptoms that last deserve a medical check. Do not assume a cold swim was harmless just because the person feels better once they are back on the boat.

The most dependable habit is to decide before you enter the water when you will get out. Set a time limit, agree on a signal with your buddy and keep dry, warm clothes where you can reach them without walking far. A cold swim that ends early with warm layers ready is a good result, not a failure, and it means the next swim can be as enjoyable as this one.