A Marlborough Sounds watchdog group wants Tory Channel closed to all commercial shipping and large fishing boats.
The narrow, rocky gap which ferries plied daily to and from Cook Strait was considered one of coastal New Zealand's most tricky areas to navigate.
Guardians of the Sounds said concern was mounting over the arrival of the new, larger passenger ferries and it wanted an alternative route in place before they set sail.
A local old-salt and Guardians' spokesperson Peter Beech said the pages of Marlborough's maritime history were littered with legends of shipwrecks, and quite a few near misses.
He said luck had so far prevented a major disaster in the often treacherous Tory Channel entrance.
"We've been worried for many years about the risk factor of using Tory Channel for shipping.
"It's basically a shortcut and they've got away with it up until now."
Tory Channel property owner, Clare Pinder said there was no margin for error for ships going through the channel entrance, marked by strong tidal currents and often treacherous seas stirred up by Cook Strait swells.
"There've been a number of quite serious near-misses at the entrance to Tory Channel.
"It's a very, very dangerous piece of water and I think it's an accident waiting to happen."
Guardians of the Sounds has drafted a new risk management policy for Totaranui/Queen Charlotte Sound.
It called for the Marlborough Harbourmaster, Marlborough District Council and Maritime New Zealand to close the shipping route through Tory Channel, and use the alternative northern entrance out of Queen Charlotte Sound.
"The time has come for the Marlborough District Council and Maritime New Zealand to face up to the fact that using Tory Channel as a shortcut is just too dangerous."
Beech said the catalyst had been KiwiRail's plans to replace the current fleet of three ferries with two new, large rail-enabled ferries from 2024.
The vessels will be about 50 metres longer than the current passenger ferries.
"What has spurred us to re-evaluate this is the prospect of these two new ferries that KiwiRail have ordered and they're going to be the size of cruise ships - they're going to be 50,000 gross tonnes.
"These are huge ships."
Beech said a shipwreck in Tory Channel would be catastrophic for passengers and devastating for the environment.
"The risk to the ecology would be immense ... it's a narrow channel so all of the beaches on either side would be covered in diesel and oil."
In 2016 the Azamara Quest cruise ship carrying 1100 people hit a rock near the entrance on its first voyage into Picton.
Damage was minor but it prompted a review of the Marlborough District Council and Port Marlborough's harbour risk assessment, and called for urgent improvement to ship pilots' training.
The harbourmaster Luke Grogan said it also forced cruise ships to take a new route in and out of the Sounds.
"We haven't had cruise ships through Tory Channel for a number of years, and all shipping essentially has gone through the northern entrance - or Totaranui, with the exception of the Cook Strait ferries."
Grogan said log ships also used the northern entrance to Queen Charlotte Sound, escorted as required by a harbour pilot.
While it was considered generally safer, adding ferries to the mix could create more conflict with increased traffic.
"There are some issues there, and there are also coastal wave patterns up in that area, plus rocks and coastline that also requires navigational expertise."
He said the idea had merit but needed close analysis. Advances in navigation technology, weather mapping and shipping engineering and propulsion systems could be used as arguments in favour of retaining Tory Channel as the ferry route.
"We really need to evaluate the risk of shipping through Tory Channel perhaps more closely and more completely than we've ever need to in the past, and that's being driven by a number of factors."
He said there was no such thing as an unsinkable ship, and the risk assessment for larger ferries in Marlborough waterways would be robust.
"How are we going to control this, how are we going to mitigate this, what needs to be done to address these concerns that have been raised through the risk assessment processes that have been completed and which are ongoing."
Maritime New Zealand said it was aware of the concerns raised by the Guardians of the Sounds and has been working with the council and harbourmaster to help address navigational safety issues in the area.
A spokesperson said it was working with interested parties to ensure any potential risks were managed in relation to planned larger ferries.
"As this work is still in its early stages, it is too soon to comment on possible options, however, we are committed to working constructively with all those involved."
Kiwirail said the proposed new ferries would have systems allowing them to operate safely in Tory Channel and the inner Sounds.
It was working with Maritime New Zealand, the Marlborough harbourmaster and local regional authorities to address navigation issues in the area.
Interislander executive general manager Walter Rushbrook said it was also talking with Guardians of the Sounds and others as the project progressed.
"The proposed new larger ferries are being designed specifically for the conditions in the Sounds including Tory Channel. Although they are larger, the hull design means they will create less wake than the current ferry fleets.
"They will also be fitted out with the latest propulsion and back-up systems, meaning they would be highly manoeuvrable."
Bluebridge said it had no one available to comment