At around 1pm on Sunday the 30-year-old Waterloo man was snorkelling off Bennett's Beach with his 28-year-old friend, also from Waterloo, when it is believed he got into difficulty.

The younger man became alarmed when his friend took a long time to come ashore and he then found a flipper washed up on the beach and called 000.

The 30-year-old was found washed up on the beach not long after. His friend attempted resuscitation until surf lifesavers from the local surf club arrived and took over, prior to the arrival of police and ambulance officers.

The Westpac Rescue Helicopter was also notified, however the man could not be revived.

Acting Crime Manager for the Lower Hunter Police Local Area Command, Peter Fox, said the water conditions were calm with a small swell at low tide when the pair went out snorkelling at 12.30pm. But a wind change may have contributed to the man's death.

"Whilst they were out there the conditions changed," Mr Fox said.

"A strong north easterly breeze had chopped up the waves."