NSW Police are mounting a court challenge to a planned 50-hour blockade of the Port of Newcastle that is expected to attract thousands of people.
Organisers Rising Tide said the event from November 22 to 24 would be one of the most significant climate uprisings on the planet, with thousands of demonstrators expected in the water in canoes and kayaks.
The Supreme Court is due on Friday to hear NSW Police's attempt to deem the in-water obstruction of the port an unauthorised assembly which would leave protesters liable to arrest.
There are major safety concerns surrounding the protest, Port of Newcastle harbourmaster Vikas Bangia said.
In an affidavit tendered to the court, Mr Bangia said he could be faced with a scenario where a ship blocked by protesters could run aground with a falling tide.
A fully laden coal ship weighs up to 160,000 tonnes and may not refloat on the following high tide, requiring the assistance of tugboats to free the vessel, he said.
"Although the wake turbulence produced by a tugboat is generally not as strong as the wake turbulence produced by the ship's propeller, it can still easily capsize a kayak or small boat," Mr Bangia said.
"That would create not only a risk of collision between a tug and a canoe or kayak, but also to persons in the water as well as the risk of a kayak being crushed between a ship and a tugboat."
A grounded ship also carries a risk its the hull becomes compromised, resulting in fuel or cargo leakage and ships usually carry between 500 to 1500 metric tonnes of fuel, he said.
"The potential environmental impacts from the spill of diesel oil in Newcastle Harbour would likely be devastating," the harbourmaster said.
The Port of Newcastle is the world's largest coal export port, sending about 144 million tonnes of the fossil fuel worth $38 billion offshore each year.
Police oppose the proposed blockade because it would lead to serious delays at the port and the risk to public and officers' safety.
NSW Police Assistant Commissioner David Waddell did not have confidence that protesters would follow directions from organisers which had been negotiated and agreed with police, and held concerns of the organisation's intention to use the protest to build capacity for future civil disobedience.
"I understand the position of Rising Tide ... is to use the proposed 2024 public assembly to purposefully break the law with a view to 'upskilling' to more sustained illegal conduct in future years," he said in an affidavit.
Midnight Oil frontman and former federal environment minister Peter Garrett and ARIA award winner John Butler are among 30 musical acts due to perform on the protest sidelines.
While organisers estimated 10,000 attendees, Mr Waddell said he believed the significant free entertainment line-up will attract a much larger audience.
"I have formed the view that the risks to public health and safety are not outweighed by the right of individuals to protest," he said.
A similar blockade in 2023 featured 3000 people in kayaks and other vessels stopping coal ships for 30 hours and resulted in more than 100 people arrested.
