Environment Southland is hoping a restricted movement notice will help prevent the spread of marine pest Asian seaweed.
It's put a controlled area notice in place in Breaksea Sound in Fiordland, with restrictions for mooring, equipment and anchoring.
Biosecurity manager Richard Bowman says the seaweed could destroy marine life, including red coral.
"The best we can do is probably to contain it… bearing in mind that its natural spread rates are relatively slow, but it can be moved quickly if it hitchhikes with vessels."
Mr Bowman says they're continuing to look at all options to control the pest, because any further spread will be dangerous.
"It's got the potential to disrupt the marine ecosystem and infect the really special places, like we have some amazing marine reserves with red corals, which are found in an almost unique environment."