Yarra Ranges Crime Investigation Unit are investigating an alleged unlawful assault at Balcombe Avenue Reserve/Mooroolbark Retarding Basin in Mooroolbark between 6.30pm and 7.30pm on Wednesday 6 December.
A male offender has allegedly assaulted a victim who was riding his bicycle through the Reserve.
Anyone with information is encouraged to contact Yarra Ranges CIU on 9739 2301.