Nine people have died in NSW waterways in recent days, as police and surf lifesavers plead with swimmers not to add to the mounting toll as dangerous surf batters much of the state's coastline.
Three people have died at the state's beaches in as many days, with some 329 rescues performed, Surf Life Saving NSW's George Shales said.
"This is the busiest period our surf lifesavers and lifeguards have experienced since the last five years," he told reporters on Tuesday.
Nine people have died at the states beaches since December 1, and another 10 nationwide.
Mr Shales is pleading for swimmers not to add to those statistics, as ex-tropical cyclone Seth plays havoc with ocean conditions.
The Bureau of Meteorology has warned abnormally high tides, damaging winds and hazardous surf conditions are stretching from the NSW Central Coast all the way through to Queensland's Sunshine Coast, with waves up to 10 metres high.
"The large swell conditions and the high tide is making it extremely dangerous for the public to enter the water in these conditions," Mr Shales said.
"If you are not a strong swimmer, do not enter the water.
"If you are a strong swimmer and you do go for a swim. .. it's important to swim between the flags.
"Do not swim alone. Do not swim at uncontrolled locations."
NSW Police have also pulled at least six bodies from waterways in recent days.
Marine Area Commander Superintendent Murray Reynolds is also warning boaties and fisherman to take care.
"One of the most difficult aspects of policing is investigating fatalities and understanding that the outcome was entirely preventable," he said.
Supt Reynolds said people should not to go rock fishing in rough conditions and anyone out on a vessel should wear a life jacket and not drink alcohol.