This week regional council contractors are clearing heavy fuel oil residue from the beach on Motuopuhi (Rat) island.

The oil spill clean-up continued in the upper harbour this week.

The combination of reasonable weather and day time low tides this week enabled more oil spill clean-up work on Motuopuhi Island.

Motuopuhi, also known as Rat Island, is only accessible on foot at low tide.

'A small team are taking advantage of favourable tide and weather conditions this week to clean-up some residual oil that had been covered by sand and has been gradually exposed by tidal movements this month,” says Regional On-Scene Commander Adrian Heays.

That work is expected to be completed today Friday.

'We're still working with iwi and hapu on completing final sign off at Maungatapu and Motuopuhi,” says Adrian.

An estimated 1.5 tonnes of heavy fuel leaked into Tauranga harbour on April 28, and driven by a rising tide and strong northerly wind, fouled the Maungatapu shore and Motuopuhi.

Clean-up operations at Matakana, and at Rangiwaea Island, Pilot Bay and Sandy Bay were signed off last month.

Shoreline assessments are signed off as complete, or conditional on some further sampling. There is some final cleaning of a few last piles at Berth 9 and some cosmetic cleaning of marina surfaces. Mobil and the Tauranga Bridge Marina are making arrangements to complete those final tasks.

The Anzac weekend oil spill is the largest Tier 2 oil spill in New Zealand, because of the time it's taken to clean it up, and the escalating cost of that clean-up, says Tauranga NZ First MP, Clayton Mitchell.

'In fact, the size of the spill, the time taken to clean and the associated costs are all so much, that we could correctly classify the spill as a Tier 3,” says Clayton.

Mobil says it won't use the pipeline for refuelling until there is full confidence in its integrity, and that it has done everything it can to mitigate the risk of another incident. This was expected to take three months.

Tauranga Bridge Marina where oil is still being cleared from marina berths, of the costs passed on by the Bridge Marina Travelift, which has been cleaning up the oiled boats that were in the marina at the time of the spill.