Mundaring police and Coronial Investigation Squad officers are investigating the death at the popular swimming spot just before 1pm.
Onlookers tried to resuscitate the man before St John Ambulance officers arrived.
Police are seeking witnesses and ask anyone with information to call 1800 333 000.
PerthNow Digital Edition.
Your local paper, whenever you want it.Get in front of tomorrow's news for FREE
Journalism for the curious Australian across politics, business, culture and opinion.
READ NOW