A 15 year-old girl who was swimming in the sea off Southbourne Beach, has been hit by a rock which was thrown towards her.
She suffered a fracture to her skull and facial fractures.
It happened at around 4pm on Monday 4 September 2023.
Police Constable Hele Leech-Wilkinson, of Bournemouth CID, said: “This incident left the young victim with nasty injuries and was understandably a very distressing experience for her.
“We have been conducting enquiries into this matter and have now spoken further with the victim and obtained additional details. I understand there were a number of other people in the vicinity at the relevant time and I am now in a position to appeal for witnesses to the incident, or anyone who may have captured relevant mobile phone footage, to please contact us.”