A 16-year-old boy has drowned after getting into difficulties while swimming in a lake.
The victim is understood to have been trying to get to an island when he got into trouble on Thursday evening.
Specialist rescue officers led by the fire service later found his body in the water at Lee Valley Park in Cheshunt, Hertfordshire.
Hertfordshire Police said the teenager was pronounced dead at the scene and there were no suspicious circumstances.
A friend of the boy, who has not yet been officially named, said: “He was trying to swim to an island and got into trouble.
“The two boys he was with tried to save him, but there was nothing they could do.”
Hertfordshire Fire and Rescue Service, which led the operation, said the boy’s body was found “after an extensive bankside and water search”.
They issued a warning to people thinking about swimming in open water.
“Now that the weather is so warm it’s very tempting to cool off with a swim,” Chief Fire Officer Darryl Keen said.
“However, even the strongest swimmer can get into difficulties and we would advise people to think carefully before swimming in unsupervised areas and look out for signs and advice about the specific dangers at the location where you are swimming.”