A 13-year-old boy died after getting into difficulty in a West Yorkshire reservoir on Bank Holiday Monday, police said.
The West Yorkshire force was called to Leadbeater Dam on Lumb Lane, Halifax, just before 3.20pm.
A spokesperson said the teenage boy was pulled from the water and taken to hospital, where he was pronounced dead.
Calderdale CID are investigating, but said there are not believed to be any suspicious circumstances.
The incident came as the UK recorded its hottest May day since the Met Office began recording data, the forecaster said.
The country also recorded its provisional all-time hottest meteorological spring temperature when Kew Gardens in south-west London hit 34.8C on Monday.
Meanwhile, the hottest May temperature could be broken again on Tuesday with an expected high of 35C across large swathes of southern England and Wales – which could even creep up to 36C, the Met Office said.
Those forecasts span the Midlands, the south-east and south-west of England, East Anglia and South Wales.
In a separate incident on Sunday, a body was found in the search for a teenage boy who got into trouble in a lake in Lincoln.
Emergency services were called to Swanholme Lakes at 2.30pm on Sunday after reports that 15-year-old Declan Sawyer had entered the water and was missing.
Lincolnshire Police said in a statement on Sunday evening: “We can update that our dive team have sadly found a body in the water at Swanholme Lakes, Lincoln.
“With agreement from the family we can share that the boy who died is 15-year-old Declan Sawyer.
“Our thoughts are with his family and we send our condolences at this incredibly difficult time.
“This is such a sad incident that will no doubt also affect many of Declan’s friends and the local community as well.”
Lincolnshire Police asked people not to speculate or share information that had not come from an official source.
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