TL;DR
The RNLI has joined the Met Office in warning about open water risks during the heatwave. UK water temperatures stay cold even in heatwaves, and cold water shock can disable a swimmer within seconds. The float to live technique reduces risk if someone falls in.
The Royal National Lifeboat Institution has joined the Met Office in warning about open water safety as the heatwave continues. UK water temperatures remain cold even during heatwaves, and cold water shock can disable a swimmer within seconds. The RNLI's Float to Live advice covers what to do if someone falls in unexpectedly.
Why UK water temperatures are dangerous
Sea, lake and river temperatures in the UK typically range from 8C to 15C in May, even when air temperatures are well above 30C. Water remains far cooler than the body because of its thermal mass and the cold deep currents below the surface.
Sudden immersion triggers cold water shock, a physiological response that includes gasping, hyperventilation and a sharp rise in heart rate. The response can disable a strong swimmer within the first 60 seconds, before any thought of swimming to safety becomes possible.
Where the risk is highest
The RNLI flags rivers, reservoirs, lakes, quarries and the coast as common cold water shock locations. Inland water is particularly dangerous because deep water can sit under apparently calm surfaces and the cold layers are not visible from above.
Beaches without lifeguards carry additional risk. The RNLI lifeguard service runs at major UK beaches during the season but does not cover every shoreline. The published lifeguard times and locations are on the RNLI website.
Float to Live technique
Float to Live is the RNLI's core safety message. The technique involves tilting the head back so the ears are submerged, relaxing the body, breathing normally and using gentle movement to maintain position until cold water shock passes.
Once the initial shock subsides the swimmer can decide whether to swim or call for help. The technique works because air in clothing and lungs makes the human body broadly buoyant. The RNLI publishes video demonstrations on its website.
What to do if someone gets into difficulty
Do not enter the water to try to rescue someone. The RNLI's advice is to call 999 and ask for the Coastguard inland or the Coastguard at the coast, and to encourage the casualty to float and grasp anything that floats.
Throw a lifebuoy, rope or anything buoyant from the bank if available. Public open water locations should have safety equipment near the entry point; check before entering the water for any reason.
Additional advice for the heatwave
Drinking alcohol around water sharply increases the risk. Most coroners' inquests into UK drowning deaths since 2010 have involved alcohol consumption before entry into water.
Group safety planning, including agreeing not to enter water unsupervised and having a designated non-swimmer monitoring the group, reduces risk. The RNLI's Respect the Water campaign aims to halve UK accidental drowning deaths.
Key facts
- UK water temperatures stay 8C to 15C in May.
- Cold water shock can disable a swimmer in 60 seconds.
- Float to Live is the RNLI safety message.
- Call 999 and ask for the Coastguard.
- Alcohol features in most drowning inquests.
FAQ
Why is cold water dangerous in a heatwave?
UK water temperatures remain at 8C to 15C in May, far colder than air temperatures during a heatwave. Sudden immersion triggers cold water shock, a physiological response that can disable a strong swimmer within 60 seconds.
What is the Float to Live technique?
Tilt the head back so ears submerge, relax the body, breathe normally and use gentle movement to maintain position until cold water shock passes. The technique uses natural buoyancy from air in clothing and lungs.
Who do I call if someone gets into trouble in the water?
Dial 999 and ask for the Coastguard. The Coastguard coordinates rescues at the coast and on inland water. Do not enter the water to try to rescue someone yourself.
Where is open water safety equipment located?
Most public open water locations have lifebuoys, throwlines or other safety equipment near the entry point. Check before entering the water for any reason. The RNLI publishes a list of lifeguarded beaches on its website.
