13/11/2023

A Temperature Guide to Safe Cold Water Swimming

Cold water swimming can be a great activity for physical and mental health. But it’s also one that should be carried out with care. Water carries heat away from the body much more quickly than air, and a sudden drop in body temperature causes a change in breathing, heart rate and blood pressure.

This is particularly risky for individuals with existing heart or breathing difficulties but still poses a threat to healthy individuals and strong swimmers. A 1977 Home Office Report revealed that 55% of annual open water deaths in the UK occurred within 3m of a safe refuge (42% within 2m), and two-thirds of those who died were regarded as ‘good swimmers’.

Here, we will look at the temperatures for cold water swimming, what happens to the body in cold water, and how to measure water temperature. We will also provide some tips for staying safe when swimming in cold water.

What temperature is cold water swimming?

There’s no official cold water swimming temperature. However, according to research, dangerous responses to cold water seem to peak in water between 10 and 15 °C. Therefore, many people consider cold water to be below 15 °C.

For reference, public swimming pools usually maintain a comfortable temperature of around 26-28 °C. Everyone is different, so many people may find temperatures much higher than 15 °C to feel cold.

What are the average UK sea temperatures?

Average UK sea temperatures range from 6-10 °C in the winter to 15-20 °C in the summer, depending on region and yearly variation. March is usually the coldest month, while temperatures reach their warmest peak in September.

How to measure water temperatures for swimming?

There’s no need to invest in a special water thermometer to check the temperature of open bodies of water, you can just use a waterproof digital thermometer. Typically used for measuring food, they’ll provide a quicker and more accurate reading, and they’re easier to read than a traditional spirit-filled thermometer.

This waterproof thermometer would make an ideal wild swimming thermometer. It’s robust and convenient for carrying while you swim. Plus, it’s easy to read with a high accuracy of ±0.5 °C. It also has a handy max/min function so you can view the highest and lowest temperatures recorded.

To measure the temperature of water, simply insert the probe a few centimetres into the water and wait for the reading to stabilise.

What are the effects of cold water on the body?

Cold water shock is the typical bodily response to entering cold water. This includes an initial sharp intake of breath, followed by hyperventilation, increased heart rate, and increased blood pressure.

For typically healthy people, the respiratory responses are the largest danger on initial immersion, which is why it’s important to keep your head away from the water upon entry. This threat is at its greatest during the first 20-30 seconds and subsides around two minutes after immersion, once the body has acclimatised.

What other risks are involved in cold water swimming?

Other negative effects of swimming in cold water can include:

Cold incapacitation — As the body loses heat, it moves its remaining heat to the core to protect the internal organs. As a result, limbs grow weak and heavy. Swimming can become difficult, easily leading to drowning. Stay closer to the shore to make it easier to get out if your muscles start to get tired.

Afterdrop — The body’s core temperature can continue to drop after getting out of the water, leading to feeling colder than when you were in. If your core temperature drops too much, it can lead to violent shivering and feeling faint. Get dried and dressed as soon as you exit the water.

Risks to pre-existing health conditions — The body’s cold shock response is particularly hazardous for those with preexisting hypertension or coronary heart disease. If you have a heart condition, high blood pressure, asthma, or are pregnant, it’s recommended to seek advice from a medical professional before starting cold water swimming.

Tips for safe cold water swimming

Choose a lifeguarded area and ideally go with experienced cold water swimmers.
Wear a visible swimming hat and use a tow float for visibility.
Wearing a wetsuit to slow down the rate of cooling and increase buoyancy.
Neoprene socks/boots and gloves will help your hands and feet stay more comfortable as you swim. A warm and waterproof hat can help your body retain heat.
Adopt an incremental approach by starting swimming outdoors in the summer.
Don’t jump or dive in. Enter the water slowly, giving your body at least 30 seconds to acclimatise after the initial cold shock response before swimming or putting your face near the water.
Don’t swim in colder water for longer than 10 minutes, and avoid using how you feel as a guide — cold incapacitation can occur with little warning.
If you have difficulty swimming because of the cold, move onto your back and move your limbs as little as possible whilst staying afloat.
Get dried and dressed in warm clothes as quickly as possible when you get out.
Avoid getting out of cold water and straight into hot water. Warming up too rapidly can cause blood to rush to your fingers and toes. This can lead to a drop in blood pressure or chilblains.

Summary

The most important thing to remember when attempting cold water swimming is the danger of cold shock in the first 30 seconds of entering water under 15 °C.

Take precautions such as swimming in lifeguarded areas and with others, taking a visible tow float, and ensuring not to jump or dive in. Avoiding swimming for longer than 10 minutes and getting dried and dressed quickly afterwards will prevent further issues such as cold incapacitation and afterdrop.

By following these measures, cold water swimming can be a fun and invigorating activity with mental health benefits.