A washout along Whanganui's Anzac Parade could cut off State Highway 4 and cause massive problems if it worsens, Mayor Hamish McDouall said on Monday.
He expressed frustration over ongoing delays of repairs following the June 2015 flooding which took out the riverside walkways and edges of the road towards the bottom of Portal Street.
Another section slumped one month later in July, taking out the footpath from Taylor St to the City Bridge.
That delayed repairs while the New Zealand Transport Agency sought an engineering solution. Repairs were expected to begin last month.
Mr McDouall said the washout made it dangerous for pedestrians and could worsen, potentially blocking SH4.
"The significance of that would be massive. Heavy trucks can't use the Dublin St Bridge," Mr McDouall said.
"I have been hammering away at this for a year and have expressed my frustrations.
"We have been expecting a start (on repairs) for several months.
"Every little bit that falls away is more taxpayer money that will need to be spent on repairs."
Mr McDouall met with New Zealand Transport Agency officials and asked if the repairs would be done in time for the washout's second anniversary in June.
"They said repairs would not now begin until September or October."
Mr McDouall said he was told the repair presented a difficult engineering solution and was not a resourcing issue.
"I have to take them at their word."
In February NZTA said the repair will include a retaining wall, made up of rock from the river bed up to 4.5 metres below the cycleway. A concrete panel will be installed from the rock wall to the cycleway and sheet piling would provide additional protection from erosion.
The sheet piling will be installed below water level and won't be visible once completed.
Cost estimates for the repair range between $2 million and $5 million and will be met by NZTA.
Ross I'Anson, NZTA Highway Manager, said the consent application for the work is with Horizons and 75 per cent complete "as we collect signatures of agreement from affected parties."
"The contractors have been stockpiling materials in preparation for the repairs and are ready to start work as soon as the consent is granted."
In February he apologised for the delays.
"We appreciate the ongoing patience of the Whanganui community while we worked to find the right design to repair this section of Anzac Parade," Mr I'Anson said.
NZTA were also working on designs for repairs to two other washouts in the district - one up the Parapara Highway and another at Upokongaro.