Boat owners are moving back to their berths at Tauranga Bridge Marina's northern piers after the last of the oil from April's spill was been removed.

An estimated 1.5 tonnes of heavy fuel oil poured into the harbour on April 27.

Tony says the boats are moving back onto A and B piers. Photo: Andrew Campbell.

Driven by a northerly gale and an incoming tide, the marina and the Maungatapu foreshore bore the brunt, with many of the berths and boats on the northern piers fouled by black sticky oil.

After more than two months of juggling the needs of boat owners and clean-up contractors, marina manager Tony Arnold is happy to announce the owners are at last able to begin moving their boats back onto their own berths.

It would have been over much sooner but for the discovery after the initial clean up that significant amounts of oil remained trapped under the floating pontoons, unable to be dislodged by normal tide action.

The solution involved bringing in a contractor's launch Lady K to use the boat's propeller wash to dislodge the oil. The boat had to be berthed sideways across the dock and was only able to work at certain stages of the tide.

The marina is constructed of floating hollow concrete blocks that Tony says are 'like a big Lego set” with solid marine growth on them underwater. The oil collected in the gaps between pontoons.

'We were finding great big gobbets of it under the pontoons amongst the oysters and heavy growth,” says Tony.

'I just wanted to acknowledge the work that Bay of Plenty Regional Council have done. Their clean up people, the contract cleaners and the commercial operators with the tugs were all brilliant and very good to work with.

Clean-up teams get to grips with the spill back in April. Photo: File.

'There were difficult conditions with the tide, and they could only work in certain directions with certain tides.

'It was a big juggling act to keep everybody happy, but we think we have got through it pretty well.”

He's also thanking the marina staff who put in a lot of extra work.

Between 60-70 boats were lifted out of the water to have oil cleaned off their hulls - a job that took about three days per boat.

But once cleaned they were unable to go back to their berths until after marina cleaning was completed.

Some went to the less affected southern marina piers, while others had to be found alternative, temporary accommodation.

'I just hope nothing like this happens again because it's still amazing just how quickly it can all go wrong,” adds Tony.

He says the spill has cost the marina about $100,000 - mainly in replacing fenders, dock lines and dock fenders.

'It adds up very quickly,” he says.