There is a push in Tasmania's north-west to save an historic rail bridge with links to one of the state's mining pioneers.

The heritage-listed bridge across the Forth River near Turners Beach was built in 1890.

It is now being decommissioned as TasRail builds a new one alongside the Bass Highway.

Chief Executive Damien White says the work is part of wider upgrades.

"We've replaced or rehabilitated three bridges already in that north-west area; over the Don River the Leven River and the Blythe, and the bridge over the Forth River will be the fourth bridge we do," he said.

"Obviously the bridge has heritage value. I understand it's one of the last remaining rail swivel bridges left in Australia so we're keen to see that it remains."

Engineer Chris Martin is leading a group of locals trying to have the wrought-iron structure converted to a shared pathway before it falls into disrepair.

"It is one of the oldest surviving swing bridges in Australia. It was interesting because Forth was one of the major harbours on the north-west coast in the very early days," he said.

"It had a reasonable deep water access up the river as opposed to places like Devonport that just had swamps."

Mr Martin says the bridge was the product of pork-barrelling by James 'Philosopher' Smith, who discovered the Mount Bischoff tin mine on the west coast.

He says prominent politicians Edward Braddon and James Fenton also played a role.

"The port was one of the key points for prosperity in their community and they lobbied very hard for the bridge to be a swing bridge so that the sailing ships of the time could continue up the river and continue using the port."

"Some of the records that I've read actually indicated that the port was that busy that they had up to seven sailing ships waiting to be loaded with palings for construction of Melbourne."

Ninety-year-old Charles Smith, grandson of James, lived in the area and has fond childhood memories.

"You had to be careful what you were doing because there was a long drop to the water and at that time there were many pigeons nesting in under the bridge and we were always very careful as children not to disturb the nests or destroy the eggs."

"One thing I was taught to do as a child was to lie down on the ground with my ear flat on the rail and you could hear the clickety-clack of the rail joints from a train coming a long while before you could even hear the train."

Almost a century on, locals are after an easier way to cross.

Mr Martin wants access built for pedestrians and cyclists.

"If it's not converted to a shared pathway I'm probably more worried about the kids and families that try to make it across the current road bridges. It's not a particularly safe method of getting between Turners Beach and Leith."

Bevin Eberhardt from the Central Coast Council estimates the refurbishment would cost at least half a million dollars.

"Seeing as it's heritage listed, there'd be some interpretation on the history of it."

Details of the project are being finalised, with a submission for funding likely to go to the State Government later this year.

While the rail bridge will not carry the heavy loads of the past century, proponents are confident it will support the community in a different way.