The fire was reported just before midnight on May 2. About 40 firefighters were needed to contain the blaze, which forced the closure of Two Rocks Road between Montebello Boulevard and Zamia Rise on Sunday.
Yanchep Sergeant Jason Macander said there had been sightings of flares above the bushland leading up to the incident.
He believed they had been set off by children who had stolen them from boats. He advised boat owners to take the flares out of their vessels when not in use.
�A lot of the kids are seeing these boats and then taking the flares,� Sergeant Macander said.
The blaze was not a threat to lives or homes, with the Department of Fire and Emergency Services declaring it all clear by Monday afternoon.