Police are monitoring two sites in Sutton Bridge amid fears over anti-social behaviour.
Parish councillors have been told that gates to the East Park picnic area, which are meant to be closed at night, are being left open, making it a magnet for boy racers and other troublemakers.
PCSO Toni Musico-Cardillo told Tuesday’s parish council meeting that, while no calls about drivers misusing the area had been received, she was aware that a resident had spoken to those involved directly.
She added: “I know it’s being used for other things. A sexual act on an evening in the picnic area was reported to the police.”
Concerns have also been raised about anti-social behaviour in Arnie Broughton Walk, where would-be troublemakers can gather behind a mound of earth.
The council wants to redevelop the area, but cannot do so until an infestation of an invasive plant called Japanese knotweed is removed