He said if the man had a cardiac arrest, the onset would have been fast and there would have been no obvious signs of distress such as "splashing about in the water or calling for help".
"It was a calm and still afternoon in the bay and none of the people swimming near or around the man reacted to his situation, suggesting it was possibly sudden and silent," Mr Mundy said.
"With millions of beachgoers each year, lifeguards will often be required to respond to a wide range of medical events that are outside of standard patrolling operations. Unfortunately, as in this case, some of those events are catastrophic and the patient cannot be revived. Our sincere thoughts are with the man's family and friends."
The man was 63 and died at Wellington Hospital, 3 News reported.
"A man came and told the lifeguards and they got him. They were doing CPR on him for about 10 or 15 minutes before the ambulance came," 12-year-old witness Navi Devgun told 3 News.
The girl said she saw a crowd of people around the man who were "working pretty hard" to try to help him.
