The person in his 50s was discovered by a variety of different windsurfers slumped over his board off the coast of Rockingham on Thursday afternoon.
Unresponsive, he was dropped at shore by fellow windsurfers, the place they activated his private locator beacon (PLB), which triggered a large response from emergency companies.
Nevertheless, paramedics couldn't revive him.
Police will put together a report for the nook.
Police are asking anybody who was within the space on Thursday afternoon and will have seen a windsurfer in misery to contact Crime Stoppers by ringing 1800 333 000.