A leading Auckland politician says a Northland shipwreck is an "environmental time bomb" capable of causing a disaster worse than the Rena oil spill.
Auckland councillor and former Auckland Regional Council chairman Mike Lee last week raised concerns with mayor Len Brown about the possibility thousands of tonnes of oil being inside the Niagara, lying 120m under water near the mouth of the Hauraki Gulf.
"All the evidence suggests we have an environmental time bomb on our hands," he said.
All the evidence suggests we have an environmental time bomb.
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"The environmental consequences of a Niagara bulkhead breakdown could be catastrophic. The damage to the Poor Knights Islands could be devastating.
"The threat to seabirds who feed in the area, including two endangered birds, the fairy tern and the New Zealand storm petrel, could potentially push them over the brink."
The Niagara lies inside the Auckland coastal marine area but Auckland and Northland regional councils, Maritime NZ, Department of Conservation and the Ministry for the Environment need to work together to contain a potential disaster, Mr Lee said. He was unaware of the potential hazard when he chaired the ARC.
The luxury liner's tanks could have held more than 4000 tonnes of fuel oil when it hit a mine in 1940 on its way from Auckland to the United States with a shipment of gold bullion.
The Rena, which was wrecked on the Astrolabe reef in the Bay of Plenty in 2011, released only 350 tonnes of oil - with disastrous results for the coast and wildlife.
After the Niagara's sinking, and again two years later when a salvage operation blew holes in the hull, a thick blanket of oil coated the nearest shorelines. Oil slicks up to 15km long and 7cm thick were reported as late as 2007, along with globs of solid oil popping up to the surface.
Northland Regional Council harbourmaster Jim Lyle said the wreck's oil posed a "low environmental risk" as it was likely it had all already surfaced or had solidified in the cold water.
A Maritime New Zealand spokesman also said the agency believed any remaining oil would be in a semisolid state.
"All spills in recent years have been monitored by Northland Regional Council and Maritime NZ and found to have naturally dispersed and broken up with no observed environmental impact," he said.
"In future, there are likely to be occasional similar reports of small amounts of oil coming from the Niagara wreck as it slowly degrades.
"While this is obviously not ideal, monitoring of these releases has shown that they are naturally dispersing [and] not causing any significant environmental impact."
But a former Tutukaka resident, shipwreck specialist and inventor of a remote-controlled survey submarine, Keith Gordon, said although leakage had been sporadic, it was a case of "when", not "if", the remaining oil would be released.
"What has leaked over the past 75 years would be very difficult to estimate," he said..
"What is more important is to try to establish how much oil still remains in the wreck and the potential for a future major disaster."