Tom Ward from the Henley Trust said he was unaware of the damage until he went to the area on Sunday.
"I went there and checked on the Sunday afternoon," he said.
"When I went everything was padlocked up again, but we have had concerns about the gate being left unlocked for one reason or another in the past."
Mr Ward said that fortunately this instance of vandalism did not threaten the birdlife at the lake because of the location away from nesting grounds.
"Where they did the hooning was in the wetlands part rather than where the bird and wildlife are.
"We've had a few incidences of vandalism, graffiti, had things smashed in the past, it seems to come and go.
"A couple of men from the Mens Shed work to keep things in order and maintain the area.
"It normally tends to be worse during the school holidays."
Mr Rossiter-Stead has confidence in council efforts to prevent another episode of vandalism.
"We don't believe there to be any effect on the wildlife at this stage and we've taken steps to help minimise the chances of a repeat," he said.