Mandurah police, sea rescue crews and surf living saving volunteers are searching for a swimmer who failed to return to shore on Saturday evening.
The missing swimmer, a 69-year-old man from the local area who regularly swims at the beach, is understood to have entered the water between Silver Sands and Madora Bay beaches about 5pm.
The rescue helicopter assisted in the search until about 9pm.
Boats are expected to continue the search until about 10.30pm.
The search will then resume at first light on Sunday.
Police are coordinating the search from San Remo, where volunteers from Mandurah Surf Life Saving club are scouring the shore.