CLEVELAND'S GJ Walter park has swelled with people opposed to plans by Walker Corp to redevelop the site.
The rally held earlier today was hosted by BirdLife Australia as part of International Migratory Bird Day.
BirdLife Southern Queensland convenor Judith Hoyle said the event was hosted ahead of the May 18 federal election to send politicians a message about the importance or protecting wildlife habitat.
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She said a terrible precedent would be set if plans to develop Toondah Harbour mudflats into a mixed-use precinct that included unit complexes went ahead.
"If we can't get this protected, our nature laws are broken," Ms Hoyle said.
"Australia is setting a terrible precedent, especially when China said they would no longer do development in the Yellow Sea.
"All levels of government are stonewalling."
Toondah Harbour is recognised as a Ramsar international wetlands of importance and is a feeding ground for shorebirds, including the critically-endangered eastern curlew.
Ongoing coastal development across the globe has been blamed for the eastern curlew's decline in numbers over the past three decades.
The bird attracted a mighty show of support as hundreds of people formed a human chain at the rally, calling for the Ramsar site to be respected.
Ms Hoyle said about 19 juvenile eastern curlews were believed to be in the area.
She said the younger birds typically stayed at the site for up to four years as they matured, later migrating via the East Asian-Australasian Flyway.
"(Adult easten curlews) breed in the Russian and Alaskan tundras and come back, over the winter, to Australia," she said.
"The adults leave first and when the juveniles are six weeks old, they make the journey to these shores, via the Yellow Sea, where they feed up for a bit.
"The adults spend more time in Australia than anywhere else, arriving in September and leaving in March."
Filmmaker Randall Wood, who documented the rally, said most bayside residents did not realise how significant Toondah Harbour was for shorebirds.
He likened eastern curlews to canaries in coal mines.
"Shorebirds are under huge pressure because of like what we are seeing here," he said.
"That's why Australia needs to say no to shore reclamation.
"It is a choice between development and these birds existing."
Mr Wood said he was directing a film about the flyways used by migratory birds and was visiting places like Russia and Germany for the project.
It is understood many migratory shorebirds that use the East Asian-Australiasian Flyway are experiencing population decline.
Mr Wood's film, which will feature Toondah Harbour, was tipped for a 2021 release, he said.
Show of support
BirdLife Australia community organiser Fiona Blandford described the turnout at GJ Walter park as amazing.
She said about 500 people attended, with half of the crowd visiting from outside the Redlands.
"We had people come up from Adelaide and Brisbane's western suburbs," she said.
Callen Sorensen Karklis, who wants to run as a candidate for division two in next year's council elections, said he opposed redevelopment plans because of impacts to the environment and ratepayers.
Mr Sorensen Karklis was at the rally earlier today.
He said extra vehicles in the area would create traffic congestion and existing businesses at Cleveland's CBD would lose customers.
He believed any plans to redevelop Toondah Harbour should be focused on improving the port rather than on creating a high-density living area.
"Not enough thought has been put into this," he said.
Walker Corp had announced last month that an environmental impact assessment for the project was getting under way.
The EIS would involve geotechnical investigations, coastal processes modelling, design of marine works and stormwater modelling.
Potential impacts on marine and terrestial ecology, fisheries, groundwater, cultural heritage noise, vibration and lighting and cumulative impacts and offsets would also be studied, with opportunities for BirdLife to present its views and facts as part of the EIS welcomed.