A single specimen of the pest seaweed undaria has been found in remote Fiordland waters.
Undaria pinnatifida was discovered on a barge at Breaksea Sound during a checking exercise involving Ministry of Fisheries, Environment Southland, Department of Conservation and MAF Biosecurity New Zealand staff.
It was the first discovery of an introduced marine pest in Fiordland.
Environment Southland biosecurity manager Richard Bowman said the plant was a mature specimen with its reproductive parts well developed.
The finding was hugely disappointing, Fiordland Marine Guardians chair Malcolm Lawson said.
"Fiordland has a special and unique marine environment and a lot of effort by various agencies has gone into protecting the area from the introduction of marine pest species."
Mr Lawson said the find reinforced the need for everyone entering the Fiordland marine area to be careful not to introduce or spread marine pests.
"It is vital that the owners and operators of boats entering Fiordland ensure their vessel hulls are clean, and that all marine equipment such as ropes, mooring lines, pots, buoys, fishing and dive gear are clean and dry."
Undaria is an unwanted organism under the Biosecurity Act and a designated pest in Environment Southland's regional pest management strategy.
It is a fast-growing seaweed that can displace native species and have major impacts on marine ecosystems. The pest was accidently introduced to New Zealand waters in the mid-1980s and has become widespread throughout the majority of the country's east coast ports and harbours.
