The body of a 15-year-old boy was recovered from Cowbury reservoir near Manchester on Saturday evening, bringing the number of water-related deaths during the UK's record-breaking June heatwave to at least seven. Greater Manchester police said the teenager had got into difficulty in the water, and his family have been informed. As temperatures soared to a provisional 37.3C in Suffolk, and the London Ambulance Service reported its busiest day ever, experts renewed warnings about the hidden dangers of open water swimming.
When the air is hot, open water such as reservoirs, rivers, canals and lakes can appear inviting. But even during a heatwave, the water remains very cold. Dr Heather Massey, an associate professor in extreme environments and physiology at the University of Portsmouth, explains that the sudden drop in skin temperature upon entering cold water can trigger an involuntary gasp reflex, rapid breathing and a sharp rise in heart rate. This is known as cold water shock, and it can cause panic, inhalation of water, and even cardiac arrest—even for strong swimmers.
“Explains cold water shock and the dangers of open water swimming during UK heatwaves, using recent drownings as examples.”
The problem is that many people underestimate this danger. After spending time in the sun, the skin becomes extremely hot, but open water locations can stay cold all year round. The contrast is what triggers the shock. During May's heatwave, there were 15 water-related deaths, and the pattern repeats every year as warm weather arrives and more people head to open water to cool down. The boy's death follows a series of drownings across the UK: a 55-year-old woman died after entering a pool at Sandwell Valley Country Park in West Bromwich; a man's body was pulled from the River Severn in Shrewsbury; a 13-year-old boy, Hayden Jones-Powell, was found in Meynell Lake in Lancashire; and a 69-year-old man died after getting into difficulty in the sea at Clacton.
For UK readers, the risks are particularly acute during heatwaves, when temperatures break records and people seek relief. Chief Inspector Helen Baxter of Greater Manchester Police urged the public: "Please avoid being tempted to cool off in reservoirs, rivers, canals or ponds." She added that everyone wants to enjoy the warm weather, but it must be done safely. The dangers apply to all open water, not just reservoirs. Even strong swimmers can be caught out by cold water shock, hidden currents, or underwater obstacles. The key safety message is to never swim alone, always enter water slowly to reduce the shock, and ideally use supervised swimming sites such as lifeguarded beaches or pools.
Q: What is cold water shock? Cold water shock is the body's involuntary response to a sudden drop in skin temperature when entering cold water. It can cause a gasp reflex, hyperventilation, and a rapid increase in heart rate and blood pressure, which can lead to drowning or cardiac arrest.
Q: Why is open water dangerous even on a hot day? Open water such as reservoirs, lakes and rivers can remain very cold even when air temperatures are high. The contrast between hot skin and cold water triggers cold water shock. Additionally, open water may have hidden currents, deep drop-offs, or underwater debris that are not visible from the surface.
Q: How can I stay safe during a heatwave? The safest way to cool off is to use a supervised swimming pool, a lifeguarded beach, or a designated outdoor swimming spot with safety measures. If you do enter open water, enter slowly to let your body adjust, never swim alone, and avoid alcohol. Always check local safety warnings.
What happens next? Police and safety organisations will continue to issue warnings as the heatwave persists. The high number of drownings already recorded this summer suggests that public awareness campaigns may need to be intensified. Any further rise in water-related deaths will likely prompt calls for more supervised swimming sites and better education about cold water shock.