Eight people died after getting into difficulties in lakes and rivers across England during a spell of record-breaking hot weather that coincided with the May Bank Holiday and school half-term, as emergency services again warned that warm air does not make cold water safe. Two teenage boys died in separate incidents in Yorkshire, including a 13-year-old boy named locally as Reco Puttock, who was pronounced dead after being pulled from Leadbeater Dam in Halifax, West Yorkshire, on Monday.

On the same day, the body of a teenage boy was recovered from a lake in Rother Valley Country Park in Rotherham, South Yorkshire. The deaths have thrown a stark light on the risks that come with the first real burst of summer weather, when people head for rivers, reservoirs and lakes looking for relief from the heat. For families and rescue volunteers, it is a pattern that repeats itself year after year, and one that can turn deadly in minutes.

Steve Cavallo, an RNLI volunteer from Pontefract, said the sudden warm spell can create a dangerous false sense of security. He said people are tempted to jump into any body of water when the weather turns warm, even though reservoirs and lakes — particularly those in former industrial sites such as quarries — can have hidden hazards that catch swimmers out.

“Unfortunately, being in a country that doesn't particularly get a lot of hot weather, as soon as we do get something warm, the temptation is there to jump in any body of water, whether it be coastal or inland rivers and lakes,” Cavallo said. “We do get these incidents every year and we're trying to educate people to try to prevent this happening.”

He added that people often do not know what is beneath the surface. “You don't know what objects are below the surface. Unfortunately people throw stuff in rivers and lakes that shouldn't be there. It's easy to get caught up in that sort of thing,” he said.

Ashley Jones said the danger starts with the water itself, which remains far colder than the air even after a sudden burst of heat. “Even though the air has warmed up – and it's warmed up really quickly (this week) – the water doesn't warm up. So it's absolutely crucial that when we get into the water, we get in slowly,” Jones said.

She warned that running, jumping or diving into cold water can trigger a gasp that may begin the drowning process. “If you were to run, jump or dive in, the first response you get is a gasp. And that big, sharp intake of air is really dangerous if there's water there. So if you're in the water and you gasp that can start the drowning process,” she said.

Jones said panic can make the situation worse. “Our heart rate goes up and our breathing goes up. And that can make us panic, and if we panic and we're splashing around that can combine to cause us to inhale and start the drowning process,” she said.

Georgia Beardmore said the majority of accidental drownings take place inland rather than at the coast, a reminder that rivers, lakes and reservoirs can be just as dangerous as open water by the sea. That is what makes this week’s deaths so grim: they did not happen in some isolated stretch of rough weather, but in the sort of inland waters that many people see as harmless on a hot bank holiday.

The warning is plain. Britain’s first major heat of the season has already brought deaths, and the biggest risk is not only the water itself but the split-second decision to rush into it. For anyone heading to a lake or river this summer, the message from rescuers is simple: cold water can still kill, even when the sun is blazing.