Water in the Bay of Plenty, which was almost devastated by the oil which poured out of the stranded container ship Rena, has returned to its former purity.
Scientists have examined more than 30,000 samples from the area and today announced that levels of Polycyclic Aromatic Hydrocarbons (PAHs) from the oil have almost disappeared.
However, they said the long-term environmental impacts are not yet known and further study needs to be carried out.
The researchers will continue to collect samples from the Astrolabe Reef to determine the extent of the damage caused by the October 2011 grounding.
More than 350 tonnes of oil spilled into the waters off the coast of Tauranga when the shipping boat ran aground in one of the worst environmental disasters in New Zealand history.
Scientists will discuss their findings with local communities in a meeting to be held at the Mount Maunganui Surf Club tonight.
Professor Chris Battershill from Waikato University is overseeing the Rena recovery monitoring programme , and said they expect to test thousands of samples over the coming months.
So far they have examined samples of kaimoana species, including tuatua, pipi, paua, kina, crabs and cockles, from along the Bay of Plenty coastline including the east coast and from offshore islands.
"We want to be able to get a full picture of how the environment has been affected and pinpoint exactly what impacts are from the Rena grounding," Battershill said.
"Shellfish are a key focus because they are one of the biggest concerns for the community. They are also a good indicator of water quality because they sit on the sea floor and act as a filter. If there are contaminants in the water it is likely you would trace these in common shellfish."
Professor Battershill said today's results are "the first pieces in the puzzle".
The focus will now lead the researchers offshore, where they will examine the damage caused to the Astrolabe Reef.
As the ship is dismantled, it will enable them to get a clearer picture of the reef itself. They will use heat mapping to check if there is any debris collecting on the ocean floor.
'No excuse for inaction' - Greens
However, some Papamoa residents said small patches of oil washed up on the beach last week.
Battershill said his team are examining this rogue oil, to see if it is fresh contamination coming from the wreck, or old oil still floating in the water.
Meanwhile, the Green Party urged caution over the results.
"The Government should not take signs of environmental recovery as an excuse for its inaction to make our coastal shipping safer," said oceans spokesperson Gareth Hughes.
"Let's not forget that it has taken thousands of volunteer hours and millions of taxpayer dollars to clean up the Rena mess.
"Over 2000 birds were found dead, which represents an estimated tenth of the total bird deaths from the oil spill.
"It will take more time for scientists to determine the long-term environmental effects of the Rena, but given the devastating short-term effects on the environment and economy, the Government should do everything it can to avoid Rena-like accidents in the future.
"The Government has done nothing to make container ship spills, like the Rena, less likely, and is actively increasing the risk of an oil spill by encouraging oil companies to conduct deep sea oil drilling in our waters."