Council director of infrastructure and environment Edith Farrell said the 120-year-old bridge spanning the Moyne River was "approaching the end of its serviceable life".

"The bridge will need to be fully replaced within the next three to five years - this is within expected time frames. The bridge remains safe for use and is assessed regularly as are all bridges in the shire," Ms Farrell said.

"Council's engineering team is already undertaking preliminary planning works associated with the bridge replacement. This work includes hydrology and hydraulic assessments, engineering service relocations and bridge design criteria.

"Our team estimates the cost to be between $5 and $6 million."

The bridge was substantially refurbished just over six years ago in late 2016, causing slight controversy by turning a 100m trip from one side of the river to the other into a 14 kilometre odyssey.

While the bridge was only out of commission for two weeks in 2016, the upcoming project will shut it to the public for many months, effectively splitting Port Fairy's main western half from the East Beach and Gardens Oval precinct.

Some of the businesses on the eastern side of the Moyne River shut or reduced their hours during the 2016 works, with one resident saying you could "shoot a cannon down Griffiths Street" it was so quiet.

Ms Farrell said the council would work hard to minimise the interruption to locals.

"It's expected there will be an extended period of closure when work to replace the bridge gets underway - when that time comes there will be significant discussions with the community and an extensive awareness campaign," she said.

The Standard understands the scale of the project will be similar to the recently completed Edwards Bridge in South Warrnambool. That project cost $4.6m and shut off access across the Merri River from February to December, 2022.

Ms Farrell said the forced replacement hadn't come as a surprise and wouldn't interrupt other engineering and repair work throughout the shire.

"This has been part of our program of works for many years and is not expected to delay other projects," she said.

"Council has already begun advocating to governments for funding for this project and will continue this week with a meeting with the Minister for Roads and Road Safety Melissa Horne."

The 2016 repairs had replaced significant sections of the bridge's substructure including eight large timber bridge bearers and 600 linear metres of decking timbers at a cost of roughly $800,000.

But Ms Farrell said the council always knew the intervention had only bought the structure another 10 years.

"The work in 2016 was for a minor part of the substructure that had failed and needed repair. When works involve the substructure the top deck needs complete removal, so a major closure was required to complete the work," she said.

"While the closure was in place, other maintenance works like replacing the decking timbers, resealing the approaches and putting an asphalt layer on the bridge deck were completed to make the most of the opportunity."