Residents have been urged not to attempt to remove graffiti on Lennox Bridge, the oldest bridge of its kind in Australia.
Work is about to start to remove graffiti from the bridge at a cost of about $16,000.
Vandals attacked the historic Glenbrook site with graffiti in early July.
"Council has engaged a specialist contractor. They will commence works in the next two weeks to remove the graffiti and replace the special coating on the bridge surfaces," said Blue Mountains mayor Mark Greenhill.
"The cost to the community is high given the specialist treatment required. Sadly, due to the age of the bridge and the resultant delicacy of the surface, we can't use the traditional graffiti removal options.
"Vandalism of this important heritage item is a crime, nothing else. I would encourage anyone who encounters the illegal defacement of public or private property to report it."
Council is currently assessing security measures at the site, to determine if they can be enhanced.
To report graffiti on council property call 4780 5000 or go online at bmcc.nsw.gov.au/eservices and complete a Customer Service Request. You can also report any incidence of graffiti by calling the NSW Graffiti Hotline on 1800 707 125 or Crime Stoppers on 1800 333 000.