Wollondilly Council and Blue Mountains Council have joined forces to rally against the state government's plan to raise the Warragamba Dam wall.
The mayors of each council area will host a community forum on Sunday, November 10 at the Blue Mountains Theatre and Community Hub (104 Macquarie Road, Springwood) from 9.30am to 10.30am.
Wollondilly mayor Matthew Deeth said he was happy to work alongside Blue Mountains mayor Mark Greenhill to oppose the proposal and protect people, property and wilderness.
"The Community Forum will highlight what is at stake with the government's proposal," he said.
"Namely breach of Native Title Agreements and the compromising of Native Title, irreversible loss of Aboriginal cultural values, loss of UNESCO World Heritage listing, extinction of threatened plants and animals, such as the Regent Honeyeater, destruction of the last Wild Rivers in NSW and the risk to quality of life for residents."
The special guest speaker at the event will be former NSW Environment Minister Bob Debus.
Residents will also have a chance to have their say or ask questions about the plan.
"It's really important to engage the community and help them to understand the key issues with this plan," Cr Deeth said.
"Not one single drop of water will be saved by raising the wall, it is simply a flood mitigation strategy.
"The council is frustrated with the lack of community consultation that has taken place with this plan."
Blue Mountains mayor Mark Greenhill said "everyone loses if they raise the dam wall".
"It will not protect people currently living on the floodplain and their property," he said.
"There are better ways to mitigate flood and the government knows that.
"This is a tactical move to open the floodplain up to rampant development, at the expense of indigenous culture and World Heritage wilderness."
Other speakers on the day include Gundungurra elder Aunty Sharyn Halls, Give a Dam manager Harry Burkitt and urban sustainability campaigner Saul Deane from the Total Environment Centre.