City of Mandurah rangers have closed Avalon Beach in Falcon due to a number of shark sightings.
Three bull sharks were spotted about 500 metres off the Yeedong Road boat ramp around 8.40am on Wednesday.
The Surf Life Saving helicopter has also sighted two sharks off Peron in Rockingham.
The two-metre sharks were swimming about 300 metres offshore around 10am.
Point Peron Beach has also been closed.
Beachgoers are reminded to be extra vigilant in the water.