An appeal has been made for information about boats breaching buoys around an artificial surf reef off Dorset.
The £3.2m underwater reef in Boscombe was closed in March after an inspection found changes to its shape.
The council suspects two sand bags were damaged by a boat propeller and are compiling evidence to submit to its insurers.
Divers repaired one of the bags while the other, which had become detached, was removed. The reef remains closed.
Bournemouth council has asked anyone who may have witnessed boats on the reef to email email@example.com
Tony Williams, member for environment and economy, said video and photographic evidence was also being reviewed to find the culprit.
He added: "I would urge boat users to make sure they are familiar with the rules of the sea before setting out on the water, and in particular observe the cardinal mark and other buoys marking the reef.
"We plan to have works [to repair the reef] started as soon as possible and will let people know when we have a definite date for this."
ASR Ltd, the firm which built the reef, is also due to carry out further refinement work in the coming months.
The reef was created to enhance waves using 55 giant sand-filled bags, which are 740ft (225m) out at sea.
The reef opened in November 2009 after lengthy delays and running over budget, as part of the regeneration of Boscombe seafront.
It has been criticised for not working properly but many traders have argued it has added to the regeneration of the once-rundown area.
The council has withheld £150,000 from New Zealand-based ASR Ltd after a specialist report found the reef had not achieved all of its objectives.
It will pay £55,000 when refinement work is finished and a further £95,000 if the improvements are successful.
ASR Ltd has denied the reef failed and said it was only one of the criteria, the wave lengths, where it had not met the requirements.