Westgate Sexual Offences and Child Abuse Investigation Team (SOCIT) detectives are investigating a sexual assault that occurred at Altona Beach last month.
A 15-year-old girl was at the pier with friends when she was approached by a man on a jet ski who offered to take her for a ride about 6pm on Friday 27 November.
The victim accepted and the man rode the jet ski into deeper waters far from the shore where he sexually assaulted the girl before returning her to the beach.
Recently, investigators have received further information of similar offending in the Altona Beach area but have so far been unable to identify the victims.
The offender is perceived to be Middle Eastern in appearance, aged in his early-30s, with dark hair and beard.
He was riding a red jet ski at the time of the incident.
Beachgoers can expect to see a highly visible police presence across Melbourne's popular beaches this summer to respond to any anti-social or criminal behaviour as part of Operation Summersafe.
Local police are working alongside the Mounted Branch, Public Order Response Team, and Water Police to ensure people enjoy the warmer months safely and responsibly.
Detectives are appealing for any victims, witnesses or anyone with further information to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppersvic.com.au
