Four teenage boys have been robbed by a group wielding a machete and a bottle while they were fishing in Dawesville on Sunday
The boys were fishing on a Estuary Road jetty, about 300 metres north of the Dawesville Foreshore Reserve around 3:15pm.
Mandurah detectives say they were threatened by four males aged between 17 and 21 years old, one armed with a machete and another with a bottle.
They group stole phones, cash and jewellery before leaving the area in an older model, dark Subaru Forester, with faded paint down the side and a plastic pod on the roof.
The teenagers walked away uninjured.
Detectives have asked anyone who may have witnessed the robbery, has dashcam footage of the vehicle or the area at the time of the robbery, or has any information is asked to call Crime Stoppers on 1800 333 000 or by making a report online at http://www.crimestopperswa.com.au.