Cold water shock 

Cold water shock is a real danger in water below 15°C.  If you do find yourself in the water, wearing a life jacket could help to save your life


What is cold water shock?  

Cold water shock causes involuntary bodily reflexes when suddenly submerged in cold water. This includes a rapid increase in heart and blood pressure that can result in cardiac arrest, even if you are in good health. A strong swimming ability will have no impact on your body’s involuntary response to cold water shock.  

Unlike hypothermia, which kills slowly as heat is gradually conducted away from the body, cold water shock can be lethal in minutes. This is due to a steep decline in core body temperature, resulting in a loss of swimming ability, unconsciousness, and ultimately death. 

When are you most at risk?  

The average sea temperature in the UK and Ireland is 12°C meaning you can be at risk all year round. Fresh water may even be below this. Due to an increase in boating and other water-based activities between the months of April and October, risks are higher at the beginning of the season.  

Sea water temperatures in the British Isles typically range from 6-10 °C in the winter to 15-20 °C in the summer depending on region and yearly variation. Always check sea temperatures before setting out on the water. 

Wide shot of man who has fallen in the water

Symptoms of cold water shock  

Symptoms of cold water shock to look out for are coughing, chest pain, troubled breathing, tiredness, and irritability. It can also induce vertigo as your ears are exposed to cold water, resulting in failure to differentiate between up and down when submerged.  

These involuntary symptoms can cause you to inhale water from gasping and drown without coming back to the surface.   

The key to surviving cold shock is being alert to the symptoms and acting quickly to protect your airways and conserve your strength. The RNLI’s advice is to float for around 60 to 90 seconds – the time it takes for the effects of the cold water shock to pass and for you to regain control of your breathing.  

If you ever recover someone from the water, they may seem okay, but may well be susceptible to secondary drowning. This can occur when even a small amount of water has entered the lungs, causing a condition called pulmonary oedema. Secondary drowning can develop from 1 to 24 hours after an incident in the water. 

How to minimise the risk of cold water shock?

Always consider the temperature of the water and wear appropriate clothing for the activity you’re doing. A correctly fitted lifejacket or buoyancy aid will help you remain calm and afloat if you do enter the water.   

The RYA also advise you clip on your ISO approved safety line when the situation and weather dictate it.  

close up shot of man lying back in water in life water

Know your limits 

Most people unfamiliar with cold water find 21°C to be quite cold. On the other hand, a competitive open-water swimmer who is used to swimming in 13°C water, will probably think that 21°C doesn’t feel very cold at all. What’s important to your safety is how you personally respond to cold water. 

Get trained 

The RYA Basic Sea Survival course will provide you with an understanding of how to correctly use liferafts and the equipment they contain, as well as techniques to survive and to be found.  

The course also includes a practical session in a swimming pool where you’ll experience entering a liferaft and staying afloat all while kitted out in wet weather gear and a lifejacket. 

The RYA Sea Survival Handbook (G43) is the official supporting text for the course.