Warrnambool Sexual Offences and Child Abuse Investigation Team are investigating a report of an indecent act in Peterborough on 11 January, Victoria Police say.
Detectives have been told a woman sunbathing at Massacre Bay about 3pm was approached by an unknown naked male.
The male was performing a lewd act before he raised his arms as he got closer to her.
The woman ran from the male and was forced to climb up a cliff face, approximately three storeys high.
The woman then saw the male walking up and down the beach before losing sight of him.
Investigators have released a facial composite an of a man they believe may be able to assist with their enquiries as well as a distinctive tattoo he may have had.
Anyone with information is urged to contact Crime Stoppers.
