Authorities are still trying to work out how they can remove a whale carcass which has been stranded in an inlet south of Sydney for a week.

The male whale’s body, estimated to be 20 metres long, first became lodged on rocks near Wattamolla Beach on September 17 before it was washed onto the sand on Monday.

Sharks have been feeding off the carcass in the remote inlet located in Royal National Park, more than 15 kilometres by car or boat from the nearest town.

The NSW National Parks and Wildlife Service has told visitors to stay out of the water.

Whale welfare group ORRCA said the whale was male but its species was yet to be confirmed.

A member of the group had estimated the whale was about 20 metres, though its position in shallow water meant no formal measurement had been taken.

Towing the carcass back out to sea is one of a range of options being considered by the NSW environment office.

But the whale’s size and the beach’s location meant disposal options were limited, a spokesperson said.

Brothers’ encounter with sharks

Two Sydney brothers, Jai and Kurt Kiggins, filmed themselves swimming near the carcass on the weekend even though sharks were nearby to feast on the dead mammal.

“As soon as we got there, there was like three great whites swimming around the boat, circling our boat, and then we decided to jump in,” Jai said.

His brother, Kurt, described it as a “once in a lifetime opportunity”.

But the brothers do have plenty of experience.

They photograph and swim with big ocean fish on a regular basis, however, their mother was not happy about this close encounter.

“We really discourage the public from doing anything like that,” Shaun Elwood, from the Royal National Park, said.

– with AAP