Jakson Stancich expected to find discarded bottles on East Beach on New Year's Day, but was not prepared for what he actually found.

He and some friends had gone to East Beach, between Houhora and Rangaunu harbours, for New Year's Eve, as did a group of younger people with trail bikes and four-wheel-drives.

"They didn't seem to do too much damage," Mr Stancich said.

"They left the next day, so a friend and I went and had a look to see what they had done. To our dismay they had left the contents of a very large bean bag. I wouldn't have minded picking up a few bottles, but that was just disturbing.

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"People need to be more aware of the impact they are having on our environment," he added.

The danger posed by polystyrene on the shoreline and in the water was highlighted when a floating dock broke free on a privately-owned island when the Cavallis were struck by Cyclone Lusi in 2014.

A group of kayakers who spent Easter exploring the normally pristine islands, off Matauri Bay, were horrified by what they said was the worst polystyrene pollution they had seen.

Richard Saysell 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 looked like food, so they ate it, and felt full, but died of starvation, he said.

DoC's Bay of Islands area manager, Rolien Elliot, said at the time that the department's major concern was for marine life such as the bottlenose dolphin, which could mistake floating polystyrene, which could block the digestive tract, for food.

More than 160 marine species worldwide have been reported to have eaten polystyrene and other litter, often resulting in starvation. Polystyrene also leaches chemicals, affecting the fish, crabs and other wildlife that might eat it.