A 17-year-old man has been arrested on suspicion of rape after a girl, 15, reported being pulled into the sea and attacked.
The boy, from Warwickshire, was arrested following a public appeal and the release of an e-fit on BBC One's Crimewatch Live.
The incident took place near Bournemouth pier on 18 July while the beach was packed with holidaymakers.
Police said the boy was "assisting detectives with their enquiries".
A statement issued by Dorset Police read: "A 15-year-old girl was with friends in the sea near to the Oceanarium when she began talking to a teenage boy.
"The boy allegedly pulled her out deeper into the sea, where he is reported to have raped her."
Detectives from Dorset Police’s Major Crime Investigation Team launched an investigation into the incident.
The attacker reportedly told his victim he was aged 17 and had travelled to the Dorset coast from Birmingham.
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He was described as having tanned skin, between 5ft and 5ft 7ins tall and of a thin but muscular build with short dark hair.
Detective Inspector Wayne Seymour, of MCIT, previously said police had "obtained forensic evidence" that meant they could "eliminate anyone who was not involved" from their enquiries.
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