New efforts are under way to convince government to salvage a massive quantity of oil trapped inside a shipwreck in one of New Zealand's most treasured marine environments.

If successful, it will be a return to the wreck which sank in 1940 with half a billion dollars worth of gold on board.

The gold has been removed but the RMS Niagara remains, sitting 120 metres below the surface with at least 1000 tonnes of oil still on board.

That's more than three times the 300 tonnes MV Rena spilled across beaches and reefs around Tauranga in 2011.

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Records examined by the Herald show there are reports of small discharges of oil over decades with some observers recording oil stretching for kilometres on the surface of the sea around wreck.

While Maritime NZ considers the Niagara to be at no immediate risk of a massive oil spill, documents released through the Official Information Act show a new plan specifically for the Niagara was developed in 2016.

Auckland councillor Mike Lee wants the oil out as soon as possible, once an exploratory mission has been carried out to check the state of the wreck and to estimate how much is actually aboard.

"The real concern is as the wreck's got older and older, the bulkheads tend to collapse in on themselves. The tanks holding this bunker oil are likely corrupt and a lot of oil will come up at once."

He has written to the new Conservation minister Eugenie Sage and Transport minister Phil Twyford to ask for their support.

First he wants the ministers to meet experts on deep-sea recovery, including, Keith Gordon, an expert on the Niagara who wrote "Deep Water Gold: the story of RMS Niagara – the quest for New Zealand's greatest shipwreck treasure".

Gordon said concern about the oil was first raised with officials 20 years ago and even though there had been surveys done it was still not known exactly how much oil remained aboard.

"It's always been out of sight, out of mind. The Rena has brought it to a lot of people's attention. The ship is on its side and is collapsing."

The depth had always been seen as a barrier but Gordon said modern technology made it achievable for a cost of around $6 million.

Responsibility for the wreck has been a juggle at times but currently rests with Maritime NZ. Auckland Council landed responsibility also when the supercity was created, with boundary changes planting the wreck squarely inside its zone.

Oddly, it always had been but a mistaken understanding of where it was had meant the Northland Regional Council had been in charge.

Maritime NZ safety manager Nigel Clifford said there was no planned monitoring of the wreck but it did receive regular reports.

"The wreck lies below one of New Zealand's busiest shipping routes and the occasional oil leaks coming from it are reported to Maritime NZ by the many vessels that use it."

The OIA documents from Maritime NZ show its concern over an oil spill is low, with sampling from 2008 showing the type of fuel would exist in a semi-solid state because of the temperature at that depth.

It meant it was unlikely to shift or discharge in great quantities.

If it did happen, then Maritime NZ's "New Zealand Marine Oil Spill Response Strategy" would kick into action, along with local supporting plans. That would see 20 depots of oil spill equipment around the country along with around the national response team, made up of 400 trained staff from councils, Massey University, and other organisations.

The Niagara was launched in 1912 as the "Titanic of the Pacific" and set out to ply its trade at ports from Australia and New Zealand to the United States and islands between.

The ocean-going passenger liner was blamed for decades as the ship to have brought the deadly influenza virus in 1918, probably because of the false rumour that passengers Prime Minister William Massey and his deputy Joseph Ward had rejected quarantine measures.

As it happened, the virus was already in New Zealand with dozens of ships arriving from Europe and the United States around the same time.

The Niagara was then relied on at a critical early point in World War II. With the bitterness of Dunkirk fresh to the British and Commonwealth war effort, the Niagara was loaded with gold to pay for supplies in the United States and weapons bound for the United Kingdom.

The war had crept closer than simply commanding New Zealand's gold and rifles. It had crept so close that there were now mines sewn in the sea off the coast of Whangarei.

They had been placed there just weeks prior to the Niagara's departure - 228 in total.

Having just left Auckland, the ship was fully-laden with gold, munitions, oil and passengers for a lengthy trip across the Pacific.

Its route took it directly through the minefield.

At 3.40am on June 19, the Niagara struck a mine. All 400 aboard abandoned ship in the 90 minutes before the Niagara slipped beneath the surface, eventually coming to rest 120 metres below.

With that, she became the first ship sunk by enemy action in the Pacific.

As Lee says: "The Germans, with that mine, scored a big hit taking out the gold and all our ammunition."

Documents held in Archives NZ show the loss of the gold was a war secret and the subject of high-level communication across the Commonwealth.

A WWII message from the NZ Prime Minister to his Australian counterpart, urging secrecy about the gold.
A WWII message from the NZ Prime Minister to his Australian counterpart, urging secrecy about the gold.

It was with great secrecy that salvage work began in December 1940 in a bid to recover the gold. The depth was beyond the edge of comfortable human endeavour so required new diving bell technology.

It also required divers with nerves of steel - not only did they use explosives to blast their way through the hull, they returned from beneath with horror tails of diving lines becoming entangled in the trigger spines of submerged enemy mines.

"How the hell we got the gold out in the 1940s shows how resourceful that generation was and the allure of gold," says Lee.

The success of the 1941 salvage operation of almost $500m in gold celebrated in a message to New Zealand government ministers.
The success of the 1941 salvage operation of almost $500m in gold celebrated in a message to New Zealand government ministers.

Brothers John and Bill Johnstone were lead divers on the recovery and became heroes of the day.

In 1953, there was another attempt with 30 bars recovered. That left five gold bars unaccounted for to this day.

In the years since, there have been repeated written queries lodged with forerunners of Maritime NZ - queries from salvage experts the world over. The remaining five bars still justify gold fever being worth around $3.5m, unless they were destroyed or similar disappeared during earlier authorised or unauthorised salvage missions. The gold still belongs to the United Kingdom.

An added layer of isolation arrived for the wreck in 1979, in the form of legislation passed to protect the submarine communications cable.

Constant queries through the years have asked after salvage rights to the Niagara.
Constant queries through the years have asked after salvage rights to the Niagara.

With the law, it became illegal to anchor over the Niagara.

Documents from the Department of Conservation and Maritime NZ from the mid-1990s show a series of officials rediscovering the existence of the wreck and the potential threat it posed.

As Gordon says, it was only with the Rena that there came a new focus on the potential risks posed.

There is also a potential added risk with warmer sea temperatures this year showing the water 2 degrees higher than normal. Records over the decades have shown an increase in reported leaks when the water gets warmer, possibly loosening the "semi-solid" state of the oil created by low temperatures, although Maritime's Clifford said there was little seasonal temperature change beyond 100m.

Associate Minister of Transport Julie Anne Genter said she had asked Maritime NZ to provide advice to both her office and the Minister of Conservation, Eugenie Sage.

"I would be concerned if there was a serious risk of oil being released from the Niagara."

A "ticking time bomb" is what Lee called the Niagara, saying the sinking was an act of war that continues to be a "clear and present danger" to New Zealand.

Auckland Conservation Board chair Lyn Mayes called it a "preventable environmental disaster".

Writing to government ministers earlier this year, she said: "It is better to act now to minimise the effects than to let the wreck totally fail in the next decade or so and have a catastrophic effect."

Other New Zealand shipwrecks

Rena: Oct 5, 2011
Grounded on the Astrolabe Reef while approaching Tauranga Harbour, the German-built Rena was the largest ship ever wrecked in New Zealand waters. No lives were lost but was NZ's costliest-ever shipwreck.

Mikhail Lermontov: 16 Feb 1986
The Soviet cruise liner hit rocks off Cape Jackson in the Marlborough Sounds, and its hull was sliced open in three places. The 155-m vessel sank at 10.45pm that summer evening. Today, the wreck has become a popular dive site.

Wahine: 10 Apr 1968
The Lyttelton–Wellington ferry Wahine's sinking is New Zealand's worst modern maritime disaster. Fifty-one lives were lost that day and another died several weeks later and a 53rd victim died in 1990 from injuries sustained in the wreck.

Liner Wanganella: 6 Feb 1947
Trans-Tasman liner Wanganella, carrying 400 passengers from Sydney, struck Barrett Reef at the entrance to Wellington Harbour at 11.30 p.m. on 19 Jan 1947. Everyone on board was safely evacuated. For 18 days the vessel was stuck fast to the reef, and on 6 February, floated clear on a southerly swell.

Turakina: 20 Aug 1940
Freighter Turakina, a British vessel, was sunk by the Orion, a German armed raider nearly 500 km off the Taranaki coast after a brief gun battle in the Tasman Sea. Thirty-six members of its crew were killed. Twenty-one survivors were rescued from the sea and taken prisoner; one soon died from his wounds.

(source: New Zealand History)