"There is strength in numbers - and we know when councils unite the government takes notice."
That's the belief of Wollondilly mayor Matthew Deeth.
Cr Deeth asked councillors to support an alliance between Wollondilly Council and neighbouring councils in an effort to fight the plan to raise the Warragamba Dam wall.
He said he was delighted that councillors unanimously supported the idea at last week's council meeting.
"The council has always had a strong stance against this proposal since it was announced," Cr Deeth said.
"The Blue Mountains council has had a similar stance so it made sense for us to join forces.
"I spoke with Blue Mountains Council mayor Mark Greenhill and he was more than happy to work together on this - they thought they were alone in this process."
Many members of the community, environmental campaigners and world heritage experts have also raised concerns about what effect raising the dam wall would have on the Greater Blue Mountains World Heritage Area, including the iconic Burragorang Valley.
Cr Deeth said both councils would work on a strategic plan and awareness campaign.
"The initial step is to hold a public information forum," he said.
"It will be a chance for the community to express their concerns.
"We know people in Warragamba and Silverdale have their concerns.
"It will also have the largest impact on the Indigenous community - they have the most to lose if this flooding occurs."
The state government's draft environmental impact statement (EIS) confirms the sides of the wall will be raised 17 metres if the plan is approved.
Cr Deeth said people need to understand that raising the dam wall was not about water storage.
"A lot of people tell us that raising the wall would help us save water but this proposal will not save us one single extra drop of water," he said.
"This is purely about flood mitigation - and there are other options out there.
"There have been other ideas proposed so we just want to explore those other options and see if they would be better than losing one of the most unique heritage areas in the world."
Cr Deeth said they hoped other councils neighbouring the world heritage area would jump on board.
"We will reach out to Wingecarribee and Oberon councils as soon as possible to give them the opportunity to be a part of the alliance," he said.
"We understand that other councils, like the Hawkesbury, might feel differently about [the dam wall plan] because it would mitigate flooding in their council area."
Cr Deeth encouraged residents to have their say.
"We know the community has a loud and strong voice," he said.
"Look at the details, make a submission."