"We have also conducted water sampling, which has confirmed the water in that area has returned to pre-spill conditions."
However, Transport Minister Steven Joyce warned the situation was still uncertain.
"You look at the fuel budget on that ship and you look at how precarious that ship is ... then we are still in a very precarious situation full stop," Mr Joyce said in Tauranga yesterday.
"There's a long way to go to get a significant tonnage of fuel off that ship and out of the way. We are nowhere near out of the woods."
Maritime New Zealand salvage head Bruce Anderson said there was every chance the vessel could still slip off the reef.
He said 1000 tonnes of oil were still on board the Rena and another 358 tonnes were either on board or lost into the sea.
He warned that more oil would leak before the operation was complete.
"When it will be released, we don't know."
While the weather was good yesterday, the sea swell was expected to rise by tonight.
Experts are sounding hopeful that the Bay of Plenty's prized fish life has fared much better than expected in what could be an up-side to the mess oil has made of its beaches.
Environmental adviser and coastal marine expert Professor Chris Battershill said that although about 300 tonnes of oil had leaked from the stranded ship, the bulk of it had washed onto land where it could be removed.
"Arguably the best sequence of events has happened because it's ended up on the beach," he said.
"We don't know absolutely, but we are thinking the prognosis for marine life is not too bad compared to other international events. We are desperate to get detailed information to support that."
Meanwhile, four MV Rena crew members who have remained in New Zealand for questioning are unlikely to face criminal charges, a shipping agent says.
Mike Hodgins, who has been helping the crew since they evacuated their ship after it ran aground, said the four men had been interviewed by Maritime New Zealand, the Transport Accident Investigation Commission and insurers but he believed they would probably not face charges.
Last week the Rena's captain and navigational officer were arrested and charged after the grounding.
Both men, who were granted name suppression and ordered to surrender their passports, were charged under section 65 of the Maritime Transport Act, which relates to operating a vessel causing unnecessary danger or risk to a person or property.
The charge carries a maximum penalty of $10,000, or a maximum term of imprisonment of 12 months.
A further 11 crew members were questioned but flew back to the Philippines.
Mr Hodgins believed the four men, whom he saw on Friday, were "a bit stressed and upset" and were likely to be flown home to the Philippines thisweek.
The Rena has been stuck on Astrolabe Reef on the Tauranga coast for 12 days, creating what has been described as New Zealand's worst ecological disaster.
So far it has lost more than 350 tonnes of oil and about 80 containers have gone overboard.
BY THE NUMBERS
* 350 approximate tonnes of oil lost
* 88 containers lost
* 500 volunteers on the beaches yesterday
* $3.5m cost of oil clean-up so far
* 618 tonnes of oiled sandy waste recovered (as of yesterday)
* 20 tonnes per hour - estimated speed of oil pumping operation
* 140 live birds recovered
* 1018 birds found dead
