Moorabbin Crime Investigation Unit detectives arrested two girls following an alleged assault at Mordialloc Beach last week.
Investigators were told the victim, a 13-year-old girl, attended the beach about 1.30pm on 17 December.
It is alleged she was approached by two girls before being assaulted near a toilet block close to Mordialloc Pier.
A man aged in his 50-60s intervened and stopped the assault.
The two girls left the area.
The victim sustained minor injuries.
Two 15-year-old girls both from the Casey area were arrested and interviewed on 26 XX December.
The pair were released pending further enquiries.
Investigators would like to speak to anyone who witnessed the assault or with dashcam/CCTV footage.
Officers are also keen to speak to the man who assisted the victim.
The investigation into the incident remains ongoing.
Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or submit an online confidential report at www.crimestoppersvic.com.au
