Emergency services attended Perth's Sorrento Beach about 10.30am on Friday after reports a male had been bitten by a shark while swimming along the coast.
Authorities searched for the swimmer from the air and sea, but he died from the attack, with his remains found in the water, WA Police said.
The Department of Primary Industries and Regional Development is investigating the incident, the second shark attack off WA's coast in five days.
A witness told the ABC she was alerted to the attack when she was walking along the beach and saw a pool of blood in the water.
City of Joondalup council has closed all beaches in the area, from Burns Beach in the north to Marmion in the south, as a precaution.
The fatality follows a shark attack on a surfer at a remote WA beach on Monday.
The man was seriously injured at Glenfield Beach, north of Geraldton in the state''s Mid West.
He was taken to the nearby Geraldton Health Campus and was now in a stable condition.
Surf Lifesaving WA's helicopter shark patrols began for summer last week.
16°C