Maritime New Zealand's director says a review of its response to the Rena grounding has shown that the agency was not as well prepared as it should have been.
An independent review conducted by Simon Murdoch and released on Tuesday says the organisation initially buckled under the pressure of the disaster.
The container ship ran aground on Astrolabe Reef on 5 October 2011, leaking at least 350 tonnes of oil into the ocean, coating beaches and wildlife. Some 267 containers were lost overboard, with debris later washing up along the coastline.
The review says that at first, Maritime New Zealand struggled to function properly at its Incident Command Centre and with the Maritime Incident Response Team. Things started to improve about five days after the grounding when a storm struck, resulting in tonnes of oil leaking from the ship.
The report said the Maritime New Zealand was not geared to cope administratively with what happened and did not prioritise resources. It said the organisation needs to be better prepared, do more training, improve its administration and engage more with communities and iwi.
Maritime New Zealand director Keith Manch said on Tuesday the agency had not experienced anything like the Rena disaster before.
"This was particularly challenging. We know now that we weren't as well prepared as we'd ideally would've liked to been, in the sense of how quickly we engaged with other agencies that could support the response with the community, with iwi, some of the media engagement."
Mr Manch said the capability to respond to incidents like this is based on experience.
A science professor who led a study into the impact of the Rena grounding says the results after two years of monitoring are a pleasant surprise.
The environmental study, also released on Tuesday, has shown that the environment has still not returned to the state it was in before the grounding, but says there have been few long-lasting impacts.
Professor Chris Battershill led the study and says some people have commented that the results are almost too good to be true.
"Similar incidents with about the same tonnage of oil going ashore, for instance Australia, where there was a different mechanism of beach clean-up - they used heavy material - there are still impacts from that.
"There have been a combination of events, I think, that combined to have the outcome that we've got now, which is a very pleasant surprise indeed."
The report says there is now little evidence of remaining oil or tar balls along the Bay of Plenty coast and the condition of marine animals has improved. However, it says Motiti Island is still an issue because of its proximity to the the wreck and further monitoring of the island has been recommended.
The monitoring was part of a $2.4 million long-term environmental recovery plan.