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People are putting themselves in danger by swimming on inflatable swans on lakes without a permit, while also being aggressive to staff and littering.
Leybourne Lakes in Larkfieldhas seen a spate of incidents during lockdown, with more occuring when there's hot weather.
Tonbridge and Malling Borough Council, which oversees the park, has been forced to call the police on several occasions and hire a security guard for the area.
Additional fences, gates and increased signage have also been installed to try and deter trouble-makers.
The councils says when staff have been called out to assist with situations, some of those involved have been aggressive when told to get out of the water.
Director of street scene, leisure and technical services, Robert Styles, said: "We are aware of a small minority of people who are not respecting the country park by causing damage, swimming without a permit and leaving litter.
"Anyone caught swimming in the lakes without first having undergone an assessment for open water is putting themselves at risk, and potentially others should they get into difficulty and need rescuing. They are also liable for an £80 fine."
A man from Essex, who sometimes fishes at the lakes but does not wish to be named, fears "someone will drown in the dangerous environment".
He said: "Adults and unsupervised children are swimming and taking to a large number of inflatable boats, inflatable swans etc. These are fragile devices easily punctured - if they go down someone will drown.
"The lakes are very deep in places, and also now have many large weed beds which could both trap swimmers legs, or contain sharp items which will easily pierce the cheap inflatables and they will sink."
He added: "This isn’t just about observing rules, someone is very likely to die there soon, then we’ll hear about “the tragedy of a youngster’s death”, but the real tragedy is it could have been prevented."
The visitor has also spotted "huge amounts of litter" on his trips, including "food wrappers, beer cans, Prosecco bottles" and nitrous oxide canisters, and describes the place as "a tip".
"I find it tragic that the area is so despoiled by visitors," he said.
Inspector Jon Turtle from a Kent Police community safety unit said: "In June we received a dozen reported incidents, which included large groups of young people and adults swimming in the lake, along with criminal damage to a gate and a fence at the site.
"Officers have attended the area on a number of occasions to engage with young people and PSCOs have already spoken to a number of individuals and their parents regarding the issues.
"On Saturday, June 27, four dispersal notices were issued to young people causing anti-social behaviour in order to help tackle the issue."
Mr Styles added: "We can only apologise to the responsible majority who respect the park rules and should be entitled to enjoy it without this kind disturbance. I would urge members of the public to support our efforts by reporting anti-social behaviour to a member of staff on site or the police by calling 101."