The cousin of a teenager who drowned in the Highgate Men’s Pond on Hampstead Heath has described how he lost sight of him under the water.

Moses Grunfeld, 19, was swimming in an out-of-bounds area of the pond on April 15 after it had closed and its lifeguards had left work for the day, St Pancras Coroner’s Court heard on Tuesday.

He and his three cousins entered the water through a side gate intended for fishermen when they saw lifeguards locking up the main entrance, the coroner was told.

Mr Grunfeld, known as Moshe to family, was not a strong swimmer and became tired after swimming just a few metres at about 5pm.

But when he swam back towards the bank, he slipped under the water.

Coroner Mary Hassell ruled that his death was accidental.

In a statement read out to court, his cousin Yitzchon Posen said: “I heard Moshe say, ‘I can’t anymore’. He didn’t sound panicked.

“I saw water splashes. I didn’t know if he was swimming or struggling.

“I shouted: are you ok? I didn’t hear a response. I then shouted three more times.

“I turned to the group and told them we needed to turn back, that Moshe was in trouble,” he added. “I was screaming as I swam to the bank to attract the attention of members of the public.

“We were shouting, ‘help, call police, someone is drowning.’”

Mr Posen said he did not see exactly what happened to Mr Grunfeld because he was not wearing his glasses.

When he did not emerge from the water, his cousins called emergency services and passers-by helped their frantic search.

His body was not found until 10.44pm on the bottom of the murky pond by police divers.

But Sgt Dominic Lillywhite said Mr Grunfeld would have already been dead by the time he arrived on the scene 20 minutes after the search began.

April 15 was an unusually hot and sunny day, but the water temperature was only about 10C.

A post-mortem examination found that the strict Orthodox Jewish theoology student, of Fairholt Road, Stoke Newington, died drowning. He did not have any heart problems and did not suffer a cardiac arrest.

None of the boys had ever visited the Heath before nor swum in any of the bathing ponds.

Bob Warnock, superintendent of Hampstead Heath, said the City of London Corporation has improved signage at the ponds since Mr Grunfeld’s death to warn the public about restricted swimming areas.

Ms Hassell told the court: “The teenagers weren’t swimming late at night but they were swimming outside of opening times at the pond and therefore, lifeguards were not on duty.

“If he had been swimming whilst lifeguards were on duty, it seems to me this awful incident would have been very different.”