The survivor was on Monday returned to the open ocean from Macquarie Harbour, where a pod of some 470 got into trouble early last week.

It was spotted at a river mouth by crews who are undertaking the grim task of disposing of some 360 carcasses at sea.

"(The whale) was very difficult to get to and all the aerial surveys indicated that they were lifeless," parks and wildlife incident controller Robert Buck said.

Rescuers "walked" the whale about 400 metres through the shallows before guiding it by boat to open ocean.

It takes the number of saved whales to 111 - the vast majority of those were freed last week but a handful have been found alive in recent days.

"It was really uplifting," Mr Buck said, adding it was his gut feel the whale had been in the same spot since last Monday's initial stranding of some 270 animals.

A further 200 whales were discovered dead further inside the harbour on Wednesday in what was the biggest mass beaching on record in Australia.

More than 220 carcasses have now been disposed of, with authorities aiming to tow the remainder out to sea before bad weather sets in on Wednesday.

The pod likely got into trouble chasing food near the coast or due to the misadventure of one or two individuals, experts say.

The stranding surpasses the beaching of about 320 pilot whales in 1996 in Western Australia.

Australian Associated Press