Two men fishing off Preston Beach, south of Dawesville, had a scare yesterday when a 4m white shark nudged their 3m dinghy.
It is not known whether the shark was being aggressive or how far offshore the men were when they encountered the predator.
One of the men told water police they quickly returned to shore.
The sighting was reported about 1.20pm.
A windsurfer also told authorities he saw a 4m white shark about 1.3km from shore in South Passage, Lancelin, about 6pm on Tuesday.
The sightings come just days after two tagged 3m great whites repeatedly set off acoustic receivers at Ocean Reef and a tagged shark activated a beacon at Garden Island.
The WA Conservation Council said the sightings were not surprising because more sharks visited between October and December, attracted by migrating whales and recovering snapper spawning in Cockburn Sound.