The body of a 15-year-old boy has been recovered from a reservoir near Manchester, as police renewed warnings about the dangers of swimming in open water during soaring temperatures.

Greater Manchester police said officers had been called to reports of a boy getting into difficulty in the water near Cowbury reservoir in Stalybridge at about 6.30pm on Saturday. A body was recovered later that evening, and was identified as the missing teenager.

The boy’s family have been informed. Police have ruled out suspicious circumstances.

At least seven people have now died in water-related incidents during Britain’s record-breaking June heatwave. Temperatures reached a provisional 37.3C (99.1F) in Santon Downham, Suffolk, on Friday after records were broken on three consecutive days.

It follows an earlier 15 water-related deaths during a spell of hot weather in May.

The London ambulance service said it had experienced the busiest day in its history as extreme heat gripped the capital this week. The service said demand on Friday was higher than during the peak of the Covid pandemic and during May’s heatwave.

A spokesperson said: “The service also responded to 688 category 1 emergencies – another record for a single day. These are the most seriously ill patients, including people in cardiac arrest or who have stopped breathing.”

Deaths from drowning often rise in May as hot weather arrives and more people head to open water to cool down. Many fatalities are thought to be triggered by cold water shock, as the water remains very cold even when the air temperature soars.

While the scorching weather has driven Britons to reservoirs, rivers, canals or ponds to cool off, Ch Insp Helen Baxter has advised the public against doing so. “This is such a sad reminder of the dangers of entering open water,” she said. “We remind the public to please avoid being tempted to cool off in reservoirs, rivers, canals or ponds.

“We all want to enjoy the warm weather – please make sure you do so in a safe way.”

Experts have repeatedly pointed out that many people underestimate the dangers of cold water shock. After spending time in the sun, the skin can become extremely hot, but open water locations such as rivers, lakes and reservoirs can remain cold, according to Dr Heather Massey, an associate professor in extreme environments and physiology at the University of Portsmouth

The sudden drop in skin temperature after entering the water can trigger an involuntary gasp reflex, rapid breathing and a sharp rise in heart rate.

“Unfortunately, this is something we see every year,” Massey said. “It’s a known problem when the air temperature increases rapidly but the water is still very cold. At this time of year, it hasn’t had time to warm up.”

Research by Bournemouth University found accidental drowning deaths were about three times higher on days when temperatures exceeded 25C compared with average UK summer temperatures.

Beyond pointing out the importance of understanding the risks of cold water, experts advise people to enter open water gradually rather than jumping in, allowing their breathing to settle before swimming. They also urge people to choose supervised locations where lifeguards are present whenever possible.

The RNLI’s “float to live” campaign advises people to roll on to their back, tilt their head back so their ears are in the water and allow their breathing to recover before attempting to move.

If someone else is in trouble, the advice is “phone, float, throw”: call 999 and ask for the appropriate rescue service, encourage the casualty to float on their back and throw them something buoyant if possible, rather than entering the water yourself.

Temperatures are expected to drop by about 5C or 6C on Sunday, producing highs of 25C to 26C on the eastern coast and around the mid-to-low 20s elsewhere.

The Met Office meteorologist Liam Eslick said: “We are starting to see some fresh air come in over the next couple of days.” A band of cloud and patchy rain in the north would push the humidity out towards the east on Sunday afternoon, he added.

Eslick said it would be a “bright sunny day for most people and it will actually feel like a typical summer’s day”, adding: “[It] will feel a lot more comfortable compared to what we saw at the end of last week.”