A floating dock that broke free from a privately-owned island during Cyclone Lusi is posing a serious threat to marine life along Northland's east coast.
A group of kayakers who spent Easter exploring the normally pristine Cavalli Islands, about three kilometres off Matauri Bay, said they were horrified by what they described as the worst polystyrene pollution they had seen.
Chunks of polystyrene, which can be fatal to marine life including sea birds and dolphins, were scattered across the Cavallis after the dock was smashed to pieces on rocks. In the worst-affected bays, vast numbers of polystyrene balls are piled up like snowdrifts.
Auckland man Richard Saysell said he had been kayaking the New Zealand coast for 15 years, and the polystyrene pollution he saw on Tuesday was the worst he had seen.
"Someone must know that this thing has broken away and allowed it to pollute the coast," he said.
Only a few weeks earlier a speaker had told his North Shore-based kayak club about polystyrene pollution and "the horrible things that can happen to sea life when they ingest this stuff".
"It looks like food to them, so they eat it, and feel full, but die of starvation," he said.
Fellow kayaker Peter Beadle said he was upset on Sunday, when he saw polystyrene scattered across the southern end of Motukawanui, the biggest of the Cavalli islands, but that turned to outrage on Tuesday when he saw the mass of polystyrene on Kahangaro Island, about 1.5 kilometres further south.
Mr Saysell said the biggest chunks of polystyrene were about a metre thick with remnants of concrete and green paint around the outside. It was breaking up into innumerable polystyrene balls that were forming snow-like drifts on the water and up the hillsides.
He said the mess needed to be cleaned up as soon as possible, before the next storm spread it further. Whoever allowed the pontoon to break up needed to be held accountable.
It was impossible to bring the polystyrene back in their kayaks. The clean-up would need a team of people and industrial-sized vacuum pumps.
The Department of Conservation's area manager Rolien Elliot said she had been made aware last week that a polystyrene-filled pontoon had broken free from Motukawaiti Island during Cyclone Lusi, last month, and broken up.
Northland Regional Council, which is responsible for coastal structures and marine pollution, had been in contact with the island's Chinese owners.
DOC and council staff were planning to head out to the islands to come up with a clean-up plan.
It was a lot bigger than a few individuals could manage, Ms Elliot added, although she knew of one upset local who had been travelling out to the islands in his boat to clean up what he could.
DOC's concerns were for marine life such as bottlenose dolphins, which could mistake the floating polystyrene for food, blocking their digestive tracts. A researcher in the Bay of Islands was keeping an eye out for any adverse effects on dolphins.
Floating plastic is also recognised as a major threat to sea turtle populations.