Topless youths were captured on CCTV breaking into the lido last Friday, and were seen damaging picnic benches and children’s artwork.
Officers have received several reports of anti-social behaviour in the area, and are conducting relevant enquiries.
A spokeswoman from Hampshire Constabulary said: ‘We were called at 5.59pm, June 17 to a report that a group of people had gained entry to Hilsea Lido and caused damage to benches.
‘Officers attended the location shortly before 6.15pm, however the group were no longer there.
‘We are aware of several reports of anti-social behaviour at Hilsea Lido and our Portsmouth North neighbourhood policing team have been conducting enquiries in order to establish the circumstances.
‘We have also been carrying out extra patrols in the area and will continue to do so.
‘No arrests have been made at the current time.’