A 13-year-old boy, Robert Hattersley, was found dead after "coming into trouble," while swimming in River Tyne near Ovingham on Monday, according to police. He was a resident of Crawcrook.

He had gone missing on Sunday after having gone to take a swim in the river. The boy is the third person to have drowned while swimming during the UK heatwave. A 16-year-old boy and a 50-year-old both died while swimming in Yorkshire in two separate incidents reported last week.

The 50-year-old man died while swimming in a reservoir, and the boy, Alfie McCraw, died while swimming in an abandoned quarry in Lancashire.

The authorities have now warned people against swimming in the hot weather and have asked them to stay indoors as temperatures are expected to hit 40ºC later this week.

"The weather is forecast to get even hotter over the weekend and into next week, but we would urge people to not be tempted to cool off in open water, unless it is a supervised area intended for swimming," said Superintendent Nick Smart, per The Independent.

The UK is reeling under severe heatwave conditions, with temperatures expected to soon reach 40 degrees Celsius. One of the hottest days was recorded on Monday, with a high of 38.1ºC reported in Suffolk. The authorities have asked people to stay indoors and not put their lives at risk.

"This incident serves as a timely reminder about the dangers of swimming in open water," added Detective Inspector Phil Hughes. "The weather is due to get hotter this week. I would urge people to not enter or swim in reservoirs or open waters."

According to local media reports, McCraw was a student at Outwood Grange Academy and was just months away from going to army college. He leaves behind his two siblings and parents.

Sheffield Children's NHS Foundation Trust has advised parents against letting their children run around in the sun and has asked them to keep them hydrated to avoid any mishaps. The Met Office has, in fact, issued a level three heat health alert for this week.

A canal in Northumberland. Image: Les Hull / Bellingham Bridge