A diving expert has called for national standards to be reviewed after six snorkelling or diving deaths in less than a week.

Australian Underwater Federation president Graham Henderson said the number of deaths in such a short period of time was unusual.

He also said the diving industry was ageing, with older people now having the will and money to take it up as a hobby, and there was a concerning variation in dive course quality.

He told AAP the Australian standards should be looked at and suggested a compulsory diving medical for people over a certain age would be worthwhile.

Mr Henderson's comments come after a man in his 40s got into trouble while snorkelling with two people off the NSW South Coast on Sunday morning.

Paramedics tried to revive him but he died at the scene.

Another man, who was scuba diving with his friends in Victoria, died after he was reported to be in distress on Sunday, while a 49-year-old Tasmanian man died while diving on Saturday afternoon.

The weekend incidents come after a 60-year-old Englishman died during a diving trip north of Port Douglas on Friday and two elderly French tourists died while snorkelling on Michaelmas Cay, north of Cairns, on Wednesday.