Authorities have issued warnings for dangerous surf conditions, including waves bigger than 4 metres, expected along much of the New South Wales coast today.
Lifesavers rescued about 150 people across the weekend, including incidents where multiple people were pulled from the water.
A 24-year-old man collapsed and was pulled unconscious from the water by his girlfriend at Hat Head beach, east of Kempsey, about 4:00pm Sunday afternoon.
NSW Police said members of the public performed CPR on the man, but he died at the scene.
The investigation would also consider whether the man had a medical episode.
He is believed to be from Kempsey.
Warnings are in place today for the Byron, Coffs, Macquarie, Hunter, Sydney, Illawarra, Batemans and Eden coasts.
Several beaches were closed over the weekend, with heavy swells and surf hitting Australia's east coast in the wake of Tropical Cyclone Gita.
Liam Howitt from Surf Life Saving NSW said swimmers, surfers, boaters and rock fishers should stay out of the water, particularly in the state's north.
"Northern New South Wales is expected to experience extremely strong conditions, with waves in excess of four metres as a result of the system pushing down from Queensland," he said.
"So as a lifesaving community, we're certainly encouraging everyone to be extremely careful before heading out and not to overestimate their ability or underestimate the conditions.
There is also a severe storm warning for heavy rainfall for parts of the South Coast and Snowy Mountains.
Search for swimmer now 'recovery' operation
Meanwhile, a recovery operation continues to find the body of a swimmer who went missing in rough surf on the NSW north coast on Saturday.
The 22-year-old man got into trouble after becoming caught in a rip at Valla Beach at Nambucca.
Surf Life Saving NSW chief executive Steven Pearce said on Sunday that authorities were preparing for the worst.
"We are no longer looking at this as a rescue operation, more as a recovery operation, so we have a significant amount for assets up there, surf life-saving assets up there," he said.
Further south on Sunday, two people were rescued after their boat sank in big swells on Sydney's northern beaches.
Local lifeguards rescued the pair at Shelly Beach at Manly, where powerful waves and swells of more than two metres were reported on Sunday morning.
Police Marine Area command has issued the following advice: