The fleet of kayaks, paddle boards and inflatable boats blocked the entrance to the Port of Newcastle, which exports millions of tonnes of coal each year.
Police said on Sunday evening that 156 adults and 14 youths had been arrested and charged with offences including "disruption of a major facility".
Protest organiser Rising Tide said it had briefly blocked a coal ship from entering the terminal, while the port operator said shipping was temporarily paused.
"I'm risking arrest and I encourage everyone who can to join me to fight for the future of my generation," demonstrator Niamh Cush, 16, told the crowd before paddling out.
"Get out there, be rascals and fight."
A succession of Australian states have passed strict laws in recent years targeting climate protests, drawing condemnation from civil rights organisations.
Climate protester Deanna Coco was jailed for 15 months after blocking traffic on Sydney's famed harbour bridge, although her sentence was later quashed on appeal.
Australia is the world's second-largest coal exporter, behind Indonesia, and has the third largest coal reserves in the world, according to official figures.
The Port of Newcastle, about two hours' drive north of Sydney, lays claim to being the largest coal export port in the world.
Each year it exports more than 100 million tonnes of coal, according to official figures.
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