PONDS on Hampstead Heath not designated for swimmers are being used to cool off during the hot weather – prompting fears over safety.

Scores of people went into the waters of the Model Boating Pond over the weekend after reports that the men’s and ladies’ swimming ponds had become too full. It follows a fortnight of soaring temperatures and left Heath rangers trying to persuade swimmers to come out of waters not watched by lifeguards.

Heath managers closed the gates of the ladies’ pond for a time on Saturday while they have kept a close eye on numbers at the men’s.

A spokesman for the City of London, which runs the Heath, said: “Entering the non-swimming ponds is extremely dangerous and these ponds do not have lifeguards present. The unsupervised ponds have uneven banks, varying depths and hazards such as reeds, weeds and objects on the bottom.”

He added: “People wishing to swim on the Heath should only use one of the three designated bathing ponds and only within opening hours. These facilities have highly trained lifeguards trained to Royal Life Saving Society standard, and are safe areas to swim.”

However, the City did not respond to requests from the New Journal for figures on how many people have used the ponds in the past fortnight, nor how many payments there had been at the “honesty” machines at the entrance to the swimming ponds.

The ticket machines caused controversy when they were installed in 2005 as many swimmers claimed the City had no legal right to charge people to use the facilities. The City have always maintained that swimmers should buy a ticket – but have not enforced the rule, and after the 2005 row agreed the ticket machines would be “self-policing”.

They set prices at £2 for a session but cash collected has been below the numbers of people who regularly swim. In 2012, City figures showed there were 180,000 visits to the ponds in a year – but the machines brought in an income of approximately £25,000.

With the huge numbers of swimmers coming through the gates during the hot weather – estimated to run into thousands – Heath managers should have collected a bumper windfall to help pay for the upkeep of the ponds and cover extra staffing costs. It is unclear how many have paid the voluntary fee.

Kenwood Ladies’ Pond Association co-chair Nicky Mayhew told the New Journal that the ticket machines, which are emptied on a regular basis, had been well used. She said: “A lot of our visitors are good about making a contribution and I see on a regular basis people paying their bit towards the upkeep of the pond.”

Regular ladies’ pond swimmer Mary Powell, who has served on the Kenwood Ladies’ Pond Association committee, added: “They had to close the gates by 5pm at the weekend. The effort the lifeguards made to keep everyone safe and manage the long queues was brilliant. They worked very hard and were, as ever, extremely professional.”