Burragorang Road at Back Creek, Belimbla Park sustained major damage during the weekend's storm event.
The culvert and road was washed away by the enormous quantity of stormwater which ran down the creek.
Trees upstream were also dislodged by the strength of the water flow.
Wollondilly mayor Matthew Deeth said crews were still working tirelessly to repair roads across the shire after the weekend's torrential downpour.
However Burragorang Road would not be re-opened for quite some time.
"Unfortunately the whole road is washed away and will need major work to reconstruct, which will mean the road is closed for a lengthy period of time," he said.
"We will know more once the engineers are able to do a more thorough assessment but we are working incredibly hard to fix it and pulling out all stops to have it done as soon as possible."
Design for the permanent reconstruction of the road is already under way and has been given the highest priority in the long list of repairs to be carried out across the shire.
The first priority is water and sewer, with Sydney Water currently working to restore these services for the local community.
"The storm has caused serious damage to our entire road network and we are working hard to carry out repairs with the safety of the community in mind," Cr Deeth said.
"I have been in contact with our local MP Nathaniel Smith who has offered his support to Council to get this progressed as an urgent priority."
Diversions are in place for light vehicles along Binalong Rd and Russell Lane.
The council will be monitoring the alternate route and carrying out repairs as required.
The council is also working to provide alternative access for heavy vehicles along Montpelier Drive and Barkers Lodge Road.