Bayside Sexual Offences and Child Abuse Team detectives are appealing for public assistance following an indecent exposure at Half Moon Bay in Black Rock.

Investigators have been told a man entered the water and approached two teenage girls who were swimming at 2pm on Wednesday, December 21.

The man pulled down his black coloured swimwear and exposed his genitals to the girls who swam away.

The male exited the water, collecting his belongings from a rock before walking in the direction of the local lifesaving club.

Investigators have released a computer-generated facial image and two images taken at the time of a man who may be able to assist with their enquiries.

The man was wearing a white hat, sunglasses, dark blue t-shirt, black shorts and pull-on work boots and has a tattoo on his upper right arm.