KiwiRail is to switch its fleet of three Interislander ferries to a cleaner-burning diesel oil before the end of the year, while it waits on its larger, greener ferries to be built and delivered.

The change of fuel, away from marine-grade heavy fuel oil, will align KiwiRail with international standards around ship pollution.

KiwiRail's Interislander general manager Walter Rushbrook made the announcement at a public meeting in Picton on Wednesday, hosted by local environmental group Guardians of the Sounds.

The group called the meeting to hear residents' concerns on the redevelopment of the town's ferry terminal, needed to accommodate KiwiRail's two new rail-enabled ferries, expected on the water by 2024.

The group planned to send some of the concerns and questions gathered at the meeting to Environment Minister David Parker.

Rushbrook says the longest ship in the current Interislander fleet, the Aratere, was modified last weekend in preparation for the switch to diesel.

KiwiRail is also working on a new computer system that will reduce the amount of smoke released when ferries started up.

'It won't fully get rid of the puff when it starts up, but you'll see a difference. Ultimately, the solution will be getting the new ships.”

The new Interislander ferries will be 'hybrids”, with diesel generators that produces electricity and batteries that stored it.

Picton residents have a lot of questions about the new ferries.

The batteries will be switched on when ferries are between Tukurehu/Mable Island and Picton to cut down on shipping fumes. Once docked, the ferries will be plugged into the national grid.

'So the [shipping] fume issue will eventually go away. From what I'm hearing today, the sooner we can do that, the better,” he says.

Rushbrook's announcement came after several attendees called for the Interislander fleet to produce less pollution now, not later. Residents have long been worried about the impact of ferry fumes.

Long-time Picton resident Andy Endersby says the current ferries blew 'thick and black” smoke over the playground on the Picton foreshore.

'It's disgusting. I know everyone says the new ferries will be cleaner and greener, but something needs to be done before then,” he says.

Another attendee says houses perched on Picton's hills could be 'blanketed in smog”, which she suspects is from the ferries.

Guardians of the Sounds chairman Paul Keating says the group will ask the Government whether it will take into account Picton's new air quality study.

Guardians of the Sounds chairman Paul Keating says the fumes are a 'major problem”.

Group members are worried the new ferries, capable of taking 410 more cars than the Aratere, will still contribute to air pollution through its idling cars.

The National Institute of Water and Atmospheric Research is currently studying 18 months worth of data from three air quality sensors in Picton to see where pollution was coming from.

An artist's impression of the new ferry terminal in Picton.

Blenheim is the only location in Marlborough to currently see its air quality monitored by the Marlborough District Council, with pollutants traced back to dust, pollen, heating or running vehicles.

Council chief executive Mark Wheeler says the study will determine if and where air quality improvements are needed.

New Zealand is set to sign Annex VI of the International Convention for the Prevention of Pollution from Ships (MARPOL) later this year. The treaty regulated emissions harmful to public and environmental health.