Oil and debris is still being cleaned from the coast of Tauranga a year after the Rena ran aground.
About 350 tonnes of oil was spilled when the 37,000-tonne container ship hit Astrolabe reef off Tauranga on 5 October 2011. More than 2000 birds perished.
Rena recovery manager Catherine Taylor of the Ministry for the Environment says small quantities of oil from the wreck are still being found on the beach.
Ms Taylor told Radio New Zealand's Morning Report programme on Friday that oil may wash ashore for at least another year, but it is not dangerous as it will naturally clear itself in time.
More than 300 containers are still on or around the wreck, which remain the owner of the ship's responsibility when they wash ashore, she says.
A researcher monitoring Little Blue Penguins at Mount Maunganui, Rabbit Island and Leisure Island estimates about a quarter of them have abandoned their burrows since the grounding.
Julia Graham says many eggs being incubated were abandoned when the adults died or had to be taken away from their nests to have oil removed.
Ms Graham says it will take at least two years to establish whether the other 25% have died or established burrows elsewhere.