Port Waratah Coal Services will face sentencing next month after thousands of litres of black water overflowed in the Hunter River.
The company plead guilty to polluting the river, but argued in a Newcastle Local court yesterday that there was no evidence of any environmental impact, The Newcastle Herald reported.
The court heard two workers were hosing off an area at Carrington Coal Terminal in April last year when they saw that a sump had overflowed into the river, a statement of facts said.
PWCS calculated that around 13,200 litres of water spilled into the river.
The polluted water contained "coal finings" and "slurry" that washed away with the movements of the river.
No pollution tests were conducted in the days after the incident.
The maximum penalty for the offence is a fine of $1 million, but is reduced in the local court to a maximum of $110,000.
The sentence will be handed down by magistrate Ian Cheetham next month.