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The latest survey of Otago Harbour shows it has not yet succumbed to the marine pest fanworm.
Because it had been found in Lyttelton's port in 2008, it was always a worry it could reach Otago, Otago Regional Council director environmental monitoring and operations Jeff Donaldson said.
A recent survey of Otago Harbour by Niwa found marine pests undaria and Styela clava (clubbed tunicate) but no new pests, such as the fanworm.
''But we still need to be vigilant.''
As part of that, the council had sent information packs to holders of mooring permits to encourage them to check their mooring lines, boat hulls and fishing equipment were not infected with any marine pests.
The packs included a photographic guide to ensure boat owners could identify the pests.
Owners of smaller vessels that stayed for longer periods in various places, especially before going on to Fiordland, had to be especially careful, as material could grow on the boats, he said.
''Cruise ships are pretty clean-bottomed vessels, as they are always on the move.''
The council had also worked with Environment Southland to develop a marine pests pathways plan for the Fiordland marine area.
''This plan is likely to have implications for boaties, commercial fishers and cruise ships leaving from the Otago Harbour to travel to Fiordland.''