The use of polystyrene around Northland's coast may be restricted in the wake of a serious environmental incident in the Cavalli Islands.
A major clean-up is expected to finish next week after Cyclone Lusi tore a floating dock from privately owned Motukawaiti Island, opposite Matauri Bay, in March.
The polystyrene-filled concrete pontoon was later smashed apart on rocks, scattering innumerable polystyrene fragments across the picturesque Cavallis. It was brought to public attention at Easter by a group of kayakers who said it was the worst polystyrene pollution they had seen in 30 years of paddling the New Zealand coast.
Initially the debris was concentrated on one small island, Kahangaro, but an apparent delay by the island's owners in starting the clean-up led to the mess spreading across the island chain.
Northland Regional Council coastal monitoring manager Ricky Eyre said he had inspected the islands again last week and found only small amounts of polystyrene remaining on Kahangaro and Motukawanui islands, as well as on the mainland north of Matauri Bay.
The dock's owners had agreed to clean up the remaining material. The job was expected to be finished next week.
"Overall they've done a pretty good job of removing it," Mr Eyre said.
The council was still investigating whether any further enforcement, such as fines or prosecution, was necessary.
Mr Eyre said polystyrene was widely used in floating docks and the like, and the Motukawaiti jetty had withstood serious storms in the past.
"But in light of this incident we are investigating its use in Northland and we may look at restrictions or stronger conditions on consents in future. It hasn't been a concern to date. It's taken this event to highlight the issue."
The clean-up costs, including council time, would be borne by the island's owners, Mr Eyre said. He urged anyone who still found polystyrene in the area to call the council's environmental hotline, 0800 504 639.
The Advocate has received anecdotal reports of the material washing up at Matapouri but the council has not received complaints beyond the Cavallis and Matauri Bay.
While polystyrene is not toxic it can kill birds and fish which mistake it for food. The material can block their digestive tracts or fool them into thinking they are full, leading to starvation.