Queensland's environment department is considering action against Indian mining giant Adani after water released from its Abbot Point facility during Cyclone Debbie contained eight times more sediment than allowed.
Adani was granted a temporary licence to assist with site water management during and after the cyclone that hit north Queensland.
But while it was only authorised to release water with sediment levels of up to 100 milligrams per litre, test samples showed up to 806mg/L of sediment.
Adani claimed none of the runoff had entered nearby wetlands.
"Adani Australia confirms that it advised DEHP of a high sediment level in a sump pond inside the Abbot Point designated area," it said in a statement.
"The ponds are part of the Abbot Point facility's measures to contain run off.
"(Environment department) officers have confirmed to Abbot Point management that there was no evidence of environmental harm post Cyclone Debbie."
But Environment Minister Steven Miles said the department was still investigating whether any of the sediment had leeched into nearby waterways.
"The initial report is based on Adani's sampling, the environment department has since done its own sampling and tests on, I think, two different occasions," Mr Miles said on Thursday.
"Those samples are now with the lab and the department will no doubt make its decisions once that information is available."
Companies breaching a Temporary Emissions Licence like the one granted to Adani face fines of $2.7 million even for accidental breaches, and up to $3.7 million for "wilful breaches".
Environmental groups have previously expressed concerns about the impact the Abbot Point terminal would have on the local environment.
Greens leader Richard Di Natale said the breach was the equivalent of "driving 300km/h in a school zone."
"We just say to the federal government, who are proposing to hand over a billion dollars of taxpayer money, think very carefully before you do that," Senator Di Natale told reporters in Brisbane.
"Stop that mine going ahead, because if that mine does go ahead, this is a taste of things to come."
Final test results are due to be released next week.
