Sydney - Gabe Watson admitted to drowning his wife during a scuba dive while honeymooning on Australia's Great Barrier Reef six years ago.

Watson, 32, avoided a murder trial before a Brisbane court Friday by entering a guilty plea to the lesser charge of manslaughter.

A witness at the inquest said the US couple appeared to embrace 15 metres below the surface before Tina Watson, 26, sank to the bottom and her bubble-wrap salesman husband swam to the surface.

It was alleged that Watson had grabbed his wife in a bear hug, turned off her oxygen supply to asphyxiate her, and turned the valve back on when she was dead or nearly dead.

The inquest found no fault with her equipment.

Prosecutor Brendan Campbell accepted the plea to manslaughter on the basis that Watson had failed in his duty as a dive buddy by not giving her emergency oxygen.

He had not inflated her buoyancy vest, removed weights from her belt or attempted to help her.

"He virtually extinguished any chance of her survival," Campbell told the court, demanding a five-year sentence with the possibility of parole only after 18 months.

Tina Watson was on only her second dive when she drowned and her husband of 11 days was a certified rescue diver.

In a videotaped statement to police, Watson, who has remarried, had described watching his wife sink, her arms stretched towards him.

He claimed she had knocked his mask off and that she sank so quickly that he couldn't reach her - claims the court rejected.(dpa)