Update, 3pm: Rangers closed the beaches around the Ocean Reef Marina for several hours today after a tagged great white shark was detected in the area.
The shark was detected at the Ocean Reef receiver several times between 8.40am and 12.24pm.
Beaches within 500m of either side of the marina were closed twice today. The beaches were reopened at about 3pm.
A shark was detected there yesterday and on Sunday, when City of Joondalup rangers closed several beaches near the harbour due to a sighting.
The Westpac Lifesaver Helicopter patrolled over Ocean Reef this morning.
On Sunday the shark was first detected at 9.30am and surfers reported seeing the large shark about 200m off the Ocean Reef beach.
It was detected again later in the day on both Sunday and yesterday.