A huge blue whale which washed up in the Far North last year has finally been reclaimed by the sea.

The 22-metre-long mammal appeared on a private beach near Mahinepua, north of Matauri Bay, in July last year. Its state and number of shark bites showed it was already dead when it washed ashore.

Department of Conservation staff visited and took samples for DNA testing but said towing the whale out to sea would be too expensive and would pose a health risk, so nature was allowed to take its course.

Even the whale's tail measured almost 5m across. PHOTO / SUPPLIED
Even the whale's tail measured almost 5m across. PHOTO / SUPPLIED

Signs were put up warning of the danger though the beach is accessible only from the sea or by crossing private land.

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Landowner Andrea, who didn't want her last name used, said the whale took more than a year to disappear completely.

In an easterly wind the smell was horrific - her family described those days as "whale days" - and forced them to hold off with plans they had at the time to use the property as a wedding venue.

At one stage fluids from the whale turned the beach septic and she had to chase away children risking their health by gathering oysters from the beach.

There were initial concerns that gases building up inside the whale would make it explode but that never happened.

Eventually the sea reduced the giant creature to a skeleton - the skull alone was the size of a small car - until even that was washed away in a recent storm.

Despite the smell and health risk, having a blue whale wash up next to their property was an extraordinary experience.

"We just lived with it. Not everyone gets a huge whale wash up on their beach," she said. "We like to think it was a happy old whale that just died out at sea and floated in."

Blue whales are the largest animals on Earth with males growing up to 25m long and females up to 26.5m. The heaviest one on record weighed 150 tonnes, more than the largest known dinosaur.

Few survived the industrial whaling era which only ended in 1966 for blue whales. Illegal hunting continued until 1972. Their maximum lifespan is thought to be between 60 and 110 years.

Meanwhile, six pilot whales which washed up on Motukawanui in the Cavalli Islands off Matauri Bay last month have also been reclaimed by the sea.

A DOC spokeswoman said the whales were already decomposing when found and few people visited the beach in winter so nature was again allowed to take its course. The carcasses had since refloated and been washed out to sea.

Whales stranded on the Cavalli Islands from time to time, she said. Two of the dead pilot whales reportedly washed up later on mainland beaches.