The death follows five drownings across Australian beaches since New Year's Eve.
ACT and NSW Police along with multiple emergency service agencies were called to Greenpatch beach at the southern shore of Jervis Bay on NSW's south coast just before 5pm on Saturday.
There had been reports of multiple people struggling to stay afloat in rough conditions.
A 34-year-old NSW man was brought back to the beach and responders started CPR but he was declared dead at the scene.
Paramedics attended to three other people but none required further medical attention.
A search for a 16-year-old boy, who went missing after a boat carrying him and two other men capsized near Barrenjoey Headland on Sydney's northern beaches, has ended.
A 47-year-old man was pulled from the water and treated by paramedics, but he died at the scene, while a 45-year-old man was winched to safety by helicopter.
Rescue crews have also called off a search for a 22-year-old man, who encountered trouble while swimming at Coogee Beach in Sydney on New Year's Day.
Patrols will continue at the two areas for the missing pair.
NSW Emergency Services Minister Jihad Dib said 10 people have drowned in the state this summer and a majority of those incidents were avoidable.
"The thing that really frustrates emergency services is being put in a position where they try and make conditions safe, and then some people make a decision to do otherwise," he said on Sunday.
"It really has to be a partnership, and we're imploring people to do the right thing: be sensible, swim between the flags, swim at patrolled locations, know your swimming ability, and don't take unnecessary risks."
Royal Lifesaving Australia reports the national summer drowning toll, which counts the number of deaths since December 1 2025, is 29 as at Saturday, January 3.
This is less than on the same date last year when 46 people had drowned.
Last summer, 139 people lost their lives to drowning across Australia between December 1 2024 and February 28 2025, the equivalent of at least one drowning death every day.
Authorities are urging the public to make water safety a priority by preparing before they leave home and remaining vigilant around the water.
Rough conditions up and down the east coast have required surf lifesavers to perform hundreds of rescues across the nation's beaches since Christmas Day.
Over the New Year period, the risk of drowning is three times greater than at any other time of the year.
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