All boaties might soon have to prove their hulls are clean in order to enter Fiordland waters, under a first-of-a-kind proposal aimed at stopping marine pests.
The Southland Regional Council is proposing the tough new rules to keep marine pests out of the area.
It will require all vessels from cruise ships to kayaks to prove their hulls are up to standard.
But some fishermen say the plan is impractical.
The council's biosecurity manager, Richard Bowman, said if the plan went ahead, vessels that weren't up to scratch would be turned away from Fiordland.
The aim would be to prevent marine pests such as seaweeds, fanworms and crabs from entering and establishing in the area.
"The standard [for boat hulls] is actually a thin layer of slime and a few goose barnacles. If it's got seaweed or other barnacles or other marine organisms attached to the hull then it wouldn't meet that test," Mr Bowman said.
"In addition to that we want gear [and] equipment to be clean, dry and free of any marine growth, and similarly bilge water should be managed according to some best practice guidance."
Otago University marine scientist Steve Wing has been studying Fiordland's waters for 20 years.
There was no other marine ecosystem like it in the world and it should be protected from pests, he said.
"You can find all the different sorts of habitats we recognise in marine ecology very close to each other."
The amount of boaties using the area has grown significantly over the years.
A number of those who frequent Fiordland's waters are commercial blue cod fishermen, represented by the Blue Cod Area 5 Association.
The association's spokesperson, Bill Chisholm, said - like the other 14 groups that made submissions to the council on the plan - it supported the pest-free vision.
But some details needed to be ironed out.
"There's some pretty significant logistic difficulties with the plan as proposed; we've identified five weaknesses which would affect our members quite significantly."
The number of boats that would need to be taken out of the water for cleaning would cause trouble, he said.
"There's going to be a problem with a bottleneck of slipway space in the Bluff Harbour, if all the boats are heading to Fiordland at once they won't be able to get their hulls cleaned all at the same time."
The association was also concerned the area defined as Fiordland coastal waters, which extended 12 nautical miles out to sea, would mean any vessels passing through the area would also have to comply.
Mr Bowman said it was likely some changes to the plan would be made.
"I think we'll need to look at amending the proposal to take into account vessels in transit that are not going to come, say, within one nautical mile of land, and I think that's a small change that we need to consider."
Overall there was strong support for the plan, he said.
Council officers would be taking into account all of the submissions before preparing a report for councillors to consider.