Boats and sailing kit at an outdoor centre have been damaged by people who broke into the grounds while it was closed due to the coronavirus lockdown.
South Cerney Outdoor, at Cotswold Water Park, has been closed since March.
Managing director Matt Pritchard said: “We retrieved about 10 boats from the lake, there was burnt grass and bonfires being made everywhere.”
Gloucestershire Police officers dispersed a group on Sunday.
Mr Pritchard added: “The bigger problem seems to be during the later part of the afternoon.
“Groups of 15-year-olds through to their mid-twenties were the bigger problem.
“They were in large groups, between five and 10 of them having drinks – if you look in the bins they’re full of cans.
“I confronted them and got a load of verbal abuse, threats and I had to call the police.
“Thankfully they came out and moved them on.”
The grounds have been cleared up by volunteers but it will cost hundred of pounds to repair the broken parts of the surfboards and sailing boats.
Gloucestershire Police confirmed officers attended the site on Sunday afternoon, where “words of advice were given and the group dispersed”.