A protest group says a proposed Point Peron marina being used as the justification for a canal housing estate will not be built - because it would be too expensive and require eight times the dredging that Elizabeth Quay did.
The Hands off Point Peron group has obtained information it says proves the proposed Mangles Bay Marina could cost as much as $1 billion to dredge.
The marina is the justification for a proposal to build a canal housing estate on surrounding land, which scientists and the community say is environmentally significant.
The dredging would be eight times the size of the $440 million excavation undertaken for Elizabeth Quay, they say, and would cost far more, having to be done underwater.
But the state government's partner in the development Cedar Woods insists the project will be "financially viable."
Hands off Point Peron says the proposed rezoning for housing does not oblige developers to fulfil their promise of the marina, despite it being the star attraction of the package as sold to media, the council and the government.
"It is now clear that this marina will not be built," Hands off Point Peron spokeswoman Dawn Jecks said.
"We are calling for the rezoning to be immediately abandoned because it would be a waste of public money and an abuse of process to continue with it given the marina's lack of feasibility.
"We are also calling for the establishment of a Royal Commission as a matter of urgency to inquire into the conduct of the proponents, and other key players."
At a public meeting of about 200 people in Rockingham on Wednesday, speakers said documents obtained under freedom of information laws, combined with those publicly available, showed even if developers sold 500 housing lots they would not make even half the cash needed for a marina.
The state government has already ruled out contributing.
The protest group said developers LandCorp and Cedar Woods would make far more money if they built more housing instead of the marina and they believed this was the developers' unspoken plan.
They said documents obtained showed Cedar Woods strong-arming the Department of Planning for taking too much time with the rezoning proposal and being "nervous and aggressive" in its attempt to "get hold of the land with as little scrutiny as possible".
It also said LandCorp chose Cedar Woods as its project "partner" on condition it paid LandCorp a "participation fee" equal to the land value, meaning LandCorp could get control without paying for the land, let alone a marina.
"People have no idea of the huge size of this development, five times the size of Elizabeth Quay on a tiny, fragile bit of land," Ms Jecks said.
Cedar Woods Property Managing Director Paul Sadleir said the company was appointed as a development partner after an open expression of interest process in 2010 and was confident the project was financially viable.
"Of course, planning approvals will allow for the business model to be finalised," he said.
He said the marina would be a "major drawcard" for the region, with a "thriving tourist hub" providing employment as well as an "exceptional waterfront lifestyle".
He said it would allow greater public beach access and rehabilitation of the degraded bushland at Point Peron.
Western Australian Planning Commission chairman Eric Lumsden said all rezoning proposals such as the one in question must be processed in accordance with planning legislation.
"The next stage of the process is public hearings where people who have previously made written submissions can make further representations to a hearings committee," he said.
"It is anticipated that this will get underway in April."