Surf lifesavers say the Sydney woman drowned trying to save her 10-year-old son from a rip at Congo Beach on January 17.

Surf Life Saving NSW CEO, Steven Pearce, said grabbing a bodyboard or even an esky lid could help prevent rescuers themselves becoming victims.

"It is a natural reaction to race into the water when we see our family and friends get into difficulty, but we're pleading with people to stop and think before diving in and to look for a nearby rescue device, or even an esky lid or bodyboard, to use as a flotation device," Mr Pearce said.

"It can make a huge difference to the outcome."

Far South Coast director of lifesaving, Cheryl McCarthy, said "it was a strong multi-agency response", but the woman could not be revived.

"It was a difficult afternoon for all, and certainly not the outcome we were looking for," she said.

"Our thoughts are with the family and friends of the woman who drowned."

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There was about 1.5m of swell at the remote beach. Ms McCarthy said the incident was a reminder that the surf could be unpredictable and deceptive.

"Even when the waves don't look exceptionally large, the volume of water moving around can take people off guard," she said.

"Rips can be there all day or appear quickly - known as flash rips. Flash rips can stay there only for minutes before they're gone again - they are equally as dangerous."

Lifesavers said this was the third incident since July 1, 2020, where a bystander had drowned while attempting to rescue someone caught in a rip. The two other recent drownings occurred at Woonona Beach, Illawarra and Frazer Beach on the Central Coast.

"On average, there are around two bystander drowning deaths per season, which make up just over five per cent of all coastal drowning deaths annually," lifesavers said.

"The average age of a bystander rescue drowning victim is 42.

"In the lead-up to the Australia Day long weekend, Surf lifesavers are reminding beachgoers to swim at patrolled locations, between the red and yellow flags.

"Since July 1, 2020, 20 people have drowned on the NSW coastline. During the 2019/20 season, 49 people drowned on the NSW coastline."

Police were told a nearby surfer assisted the mother and her 10-year-old son back to shore, where they were pulled from the water by witnesses.

"There was a significant response from the local Congo community and visitors as well," a police spokesman said.

Witnesses commenced CPR until NSW Ambulance paramedics and a Westpac Lifesaver Rescue Helicopter crewman arrived and took over the resuscitation.

Moruya Surf Life Saving Club volunteers responded to the scene in an inflatable rescue boat and assisted with CPR. The Toll Air Ambulance also responded.

Despite emergency services' efforts, the woman was unable to be revived and died a short time later.

The 10-year-old boy was assessed by paramedics and was uninjured.

Far South Coast volunteer lifesaver numbers have been strong on the beach this year, says Ms McCarthy.

She encouraged beachgoers to swim at patrolled beaches, between the red and yellow flags.

"Come and visit us and talk to the team; we are happy to tell you about rips and local conditions - we're always happy to chat," she said.

The nearest patrolled beaches to Congo are Moruya Main Beach and One Tree Beach, Tuross Head, less than 20km away.