Conservationists are warning a $2.7 billion residential and marina development on the banks of Caboolture River, north of Brisbane, will spell disaster for Moreton Bay.

The Queensland government has been urged to back away from its pre-election commitment to give Priority Development Area (PDA) status to the 570-hectare North Harbour site at Burpengary.

A PDA declaration would fast-track the approvals process for the project, which proponents said would house 10,000 residents and deliver thousands of construction and marine industry jobs.

But conservationists warned the project was a threat to Moreton Bay's fragile ecosystem.

Lower reaches of the Caboolture River form part of the Moreton Bay Marine Park and most of the tidal reach of the river falls within the Deception Bay Fish Habitat Area which is home to a diverse range of fish species.

'Coming to a tipping point'

Environmental scientist and water expert Ian Bell has been arguing against the marina for well over a decade.

He said his major concern was the disturbance of acid sulphate soils stirred up by the plan to dredge 5 kilometres of the lower reaches of the Caboolture River, which enters Moreton Bay.

"As soon as you expose this material to the air, the sulphurs in the soil, combined with the iron in it, creates sulphur dioxide gas and hydrogen sulphide gas — they're poisonous," he said.

Mr Bell said it would further exacerbate the growth of lyngbya — an algae responsible for fish kills.

"How can I not be concerned? I love the Bay— I've seen the deterioration of it over 50 years and we're coming to a tipping point," he said.

'Very fragile ecosystems'

The site is also near the boundary of a declared Ramsar site, a wetland of international significance and home to threatened migratory birds, including the critically endangered Eastern Curlew.

Birdlife Southern Queensland convenor Judith Hoyle said bird populations were already being impacted by other developments in the southern region of Moreton Bay.

"We'll see a level of disturbance through the build process … and increased watercraft going through these areas will disturb the birds," Ms Hoyle said.

"It's so important for these birds to be able to feed uninterrupted.

"Every time they have to fly, they are losing reserves that they need for their epic migrations back to the Russian and Alaskan Arctic."

She said the organisation had written to the state government urging it to at least dramatically scale back the project.

Declared a 'state significant' project

During last year's election campaign, Premier Annastacia Palaszczuk committed to declaring the precinct a PDA, allowing local planning frameworks and by-laws to be suspended.

It will also enable the proposal to be assessed under the Planning Act 2016.

At the time, Ms Palaszczuk said "the mechanism is designed to unlock out-of-the-box projects like this, that have the potential to create significant economic and community benefits".

"Approving a PDA would support the construction and development sector by stimulating new marine industry, tourism, retail, commercial, residential development, as well as significant community infrastructure," Ms Palaszczuk said.

Plans for North Harbour were first lodged in 2002 and the project was later declared state significant and got a conditional tick of approval from the Queensland Coordinator-General in 2009.

At the time Moreton Bay Regional Council opposed the marina development, fighting it in the Land and Environment Court.

But the council had a change of heart, with Mayor Peter Flannery saying it would create thousands of jobs and stimulate the local economy.

"They've tried to address them by moving the marina further south and to the east."

Cr Flannery said there would be an "improvement in the water quality" through protection of the riverbanks from erosion.

"We want to create jobs, we want to stimulate the economy, we want to provide for the people in the northern part of our region, for decades to come," he said.

Much-needed housing supply

The developers behind the project, North Harbour Holdings and Trask Land Corporation, said alongside increasing much-needed housing supply, the declaration of a PDA would ensure increased employment and training opportunities in the marine and construction industries.

Project director Bryan Finney said it was the only suitable location for a marina between Brisbane and the Sunshine Coast.

He said core samples taken in the river indicated it was mostly "coarse grain sand", which could be used for "environmental improvement activities such as replenishing the beach and foreshore at Beachmere".

The developers are aiming to have the project finished by 2035.

A spokeswoman for the Queensland government said there was no timeframe on when the PDA would be formally declared.