NSW Ambulance originally said the group were scuba divers.

Less than two hours later, a swimmer, believed to be in his 60s, died at Boomerang Beach near Forster on the NSW Mid North Coast.

NSW paramedics said the man was swimming between the flags. He was pulled from the water just before 2pm.

Passers-by performed CPR on the man, but he was unable to be revived and he was pronounced dead at the scene.

The death comes after a 38-year-old man died while snorkelling at Clovelly Beach on New Year's Day, with police investigating the possibility that he had a medical episode.

On Christmas Day, a man died while snorkelling at Lake Conjola on the NSW South Coast.

The 46-year-old Korean national, who was in Australia on a student visa, had been snorkelling at the eastern end of the lake when his family noticed he was missing and raised the alarm.

Last Wednesday, a two-year-old girl drowned and two other children were taken to hospital after a tragic evening in waters around NSW.