An endangered leatherback sea turtle that washed up in Pigeon Bay, in the Banks Peninsula, earlier this week is now on its way to Te Papa in Wellington.

The male leatherback weighed approximately 200kg and is believed to have already been deceased when it washed up on the beach.

Department of Conservation (DOC) Biodiversity Ranger in Akaroa Derek Cox told the Herald the cause of death is not yet known. "It could have been old age, it could have been plastic, or fishing nets," he said.

This is the third leatherback Cox has seen washing up in the area in 12 years.

The process of getting the sea turtle's body to Te Papa, currently underway, has been challenging.

The sea turtle was first reported to DOC when it was found on Monday by the owners of the Annandale villas nearby.

"I went for a drive out there initially to get photos and take measurements," Cox said.

He contacted the DOC marine team in Wellington who told him Te Papa would be interested in the sea turtle.

The turtle was floating with the tide but Cox managed to drag it and secure it to the beach on Monday afternoon.

The leatherback sea turtle on the back of the DOC truck. Photo / Supplied

However, on Tuesday, when the ranger returned to the beach, the body of the sea turtle had floated on.

"I had to go for a swim, which is not how I expected my day to go," he recalls.

With such a heavy animal, the rescue back to dry land "took a little bit".

A farmer with a tractor then helped Cox load the sea turtle onto the back of his truck and the ranger drove it back to Akaroa Harbour.

On the way back to HQ, however, he made a very important stop at the local primary school, so the children could have the chance to admire the animal.

"They all loved it, thought it was really neat," Cox said.

The next few hours were spent trying to find a nearby business able to keep the sea turtle's body frozen, or at least chilled. However, due to safety concerns, most businesses with big freezers were food businesses who could not help. Eventually, a pet food company took the sea turtle in, fully bagged up and labelled.

A curator from Te Papa is reportedly currently en route to Akaroa to pick up the animal.