The incident happened at Bournemouth beach on Sunday, July 18 last year.
Police received a report that a 15-year-old girl was raped in the sea near to the Oceanarium at around 4pm.
Detectives from Dorset Police’s Major Crime Investigation Team (MCIT) have been carrying out enquires into the incident.
Following an extensive investigation, an 18-year-old man from the West Midlands has been arrested on suspicion of rape.
He has been released on police bail as enquiries continue.
Detective Inspector Wayne Seymour, of MCIT, said: ‘We have continued to support the victim and her family throughout this investigation, and they have been updated with this latest development.’
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