Boaties and cray fishers are being asked for their help to stop a highly invasive kelp spreading around Northland harbours.
Undaria pinnatifida has made itself at home in Rangaunu and Houhora harbours.
The seaweed, which resembles some native kelps, is also known as Japanese or Asian kelp and is farmed in parts of Asia and Russia where it is used as a vegetable and in skin products.
Nicknamed ''the gorse of the seas'', it is established in Fiordland where it is seen as a threat to the unique marine environment. It is believed to have settled in several parts of New Zealand's coast over the past 20 years.
Don McKenzie, biosecurity manager for the Northland Regional Council (NRC), said it was first detected in Rangaunu and Houhora harbours about three years ago.
"It's a serious biosecurity issue because it can be hard to distinguish from native kelps, is fast-growing and in other parts of New Zealand has already impacted on the aquaculture industry, fouling mussel lines and other equipment."