The Great Barrier Reef Marine Park Authority has until Friday to decide whether to allow a massive dredging project to expand a Queensland coal mine.

Some warn it will be the death toll for the Great Barrier Reef, others say it will bring a golden age of prosperity to Queensland.

Friday is D-day for the controversial Abbot Point coal port expansion near Bowen, south of Townsville.

The project involves the dumping of three million cubic metres of dredged spoil within the marine park area to expand the port.

Federal Environment Minister Greg Hunt approved the project in December, subject to what he says are strict environmental conditions.

But the Great Barrier Reef Marine Park Authority (GBRMPA) has the final say over whether the dredge spoils can be dumped in the park – the only disposal option that’s on the table.

It must make a decision by Friday.

Environmentalists say the spoil will damage marine life and coral and expanding the port will turn the reef into a shipping super-highway.

They’ve spent months campaigning through social media, petitions and protests trying to stop the project.

Paul Oosting, from campaign group GetUp, says dredging could also jeopardise the state’s reef-based tourism industry.

“The flow-on effects are really worrying both in terms of the health of the Great Barrier Reef, its World Heritage status and importantly people’s livelihoods,” he told AAP.

The United Nation’s environment arm UNESCO says they’re reviewing the federal government’s decision to allow the Abbot Point expansion to go ahead.

North Queensland Bulk Ports, the corporation that has proposed the dredging project, has said dredging could possibly make the water cloudy during a short period and may damage seagrass but it’s unlikely to affect other flora and fauna.

They say dumping the spoil in the water will be less damaging to the environment than depositing it on land.

But green groups argue they’re opting to dump it at sea because it costs less.

A Bulk Ports spokeswoman says it may not be as simple as granting or rejecting a dredging permit – conditions could be attached, which the firm would need to address.

GBRMPA, which isn’t commenting until a decision has been made, could also outline other locations that spoil could be dumped.

If the permit is rejected altogether there could be wider implications for the mining firms looking to exploit coal resources in the Galilee Basin.

Initial approvals have been granted to Warratah Coal-China First and GVK Hancock to mine in the basin.

Coal from both mines would be transported to Abbot Point for export.

If the expansion goes ahead, an extra 70 million tonnes of coal each year – worth $1.4 billion to $2.8 billion – would go through the port.

Warratah Coal managing director Nui Harris says there are a number of options available to the mining firms if the expansion doesn’t go ahead.

Both sides are waiting for GBRMPA’s decision, which is now only hours away.