Plans to expand Picton's ferry terminal would place a heavy burden on its environment unless properly managed, a seagoing marine engineer says.
A major upgrade is planned to accommodate the new-generation of ferries which cross Cook Strait, and would include a new cruise ship berth almost right in front of the township.
Concern was brewing about the potential for more pollution to billow from larger ships docked at the wharf.
Brent Yardley lives in the Marlborough Sounds, worked on ships' engines, and studied atmospheric pollution as part of his engineering degree.
He said the air pollution produced by ships was often trapped in the surrounding hills, and was likely to get worse.
"Well what triggered my concern was what I was seeing with the inter-island ferries, but this is adding insult to injury.
"The proposed cruise ship berth in Picton is going to be on the town side of the existing ferry terminal, so you're parking ships very close to town."
Yardley said a cruise ship tied to the dock could be a bigger polluter than a ferry or cargo ship.
"The stand-out difference with a cruise ship is that it has a very, very high - what you call hotel load, for all the cabins and all of the services for the cabins, you have a lot of electrical demand.
"They have to run big diesel generators to keep that going."
Kevin O'Sullivan heads marketing authority Cruise New Zealand and said once-quiet Picton would only get busier once the international cruise industry was back on its feet.
"Picton was a relatively small place, and then once ships started to find how good it was... so yeah, absolutely, Picton and the whole of the Marlborough region is great for cruising."
Yardley wants to see Marlborough follow Fiordland's example in how it managed emissions from cruise ships, with its long-standing Deed of Agreement.
"Fiordland are proactive, they have provisions in place and they seem to be communicating their expectations - we don't have that same level of engagement in Marlborough."
Cruise ships operating in Southland waters must have a resource consent, or sign the deed before arriving in Fiordland.
Kevin O'Sullivan, the former Southland harbourmaster, helped draft it.
"It dealt with a particular set of circumstances that were unusual for Fiordland, and would probably be difficult to put in place anywhere else."
The Marlborough District Council said Picton, unlike Fiordland, was an established commercial shipping area that also handled freight and cargo.
Councillor David Oddie said since that Deed was signed councils had become a lot more aware of environmental responsibilities.
He said Yardley was right about aspects of the proposed terminal. But steps were in place to mitigate his and others' concerns, including that cruise ships coming into port adhered to an international agreement on light fuel use.
New Zealand had ratified several conventions of the international treaty for regulating marine pollution from shipping (MARPOL), but was yet to sign up to the convention that related specifically to the reduction of air pollution in ports and harbours.
The process for doing this was being led by the Ministry of Transport.
Oddie said other mitigation steps for Picton were being led by the proposed new ferries, include plugging them into a power source when they arrived.
Yardley said it was a good idea, but raised a new set of challenges, including that one cruise ship might use more power in a day than the town itself.
"If the cruise ships can be provided with a shore power connection, then they can shut down their engines, which would otherwise be running all day long.
"It's a good measure, but it does require investment."
Oddie said creating the infrastructure would be up to the lines company and the shipping sector.
"As far as council goes, it comes down to who pays for this infrastructure; it shouldn't be a ratepayer problem as much as clean air is a ratepayer issue, but this should be directly attributed to that industry."
Oddie said data from a year-long study on Picton's air quality was currently with scientists, with results expected soon.