The Queensland Government is investigating whether Indian mining firm Adani has breached its environmental licence for the second time in two years with the release of coal-laden floodwaters from its coal port at Abbot Point in the state's north.

Key points: Adani has not applied for an emergency water release permit for Abbot Point

Adani has not applied for an emergency water release permit for Abbot Point Water flowed into Caley Valley wetlands this month after monsoonal rain

Water flowed into Caley Valley wetlands this month after monsoonal rain The Queensland Government is prosecuting Adani over a 2017 wetland water release

It comes as Adani revealed it did not apply for an emergency permit to dump more polluted water into the sensitive Caley Valley wetlands during the north Queensland floods last week.

The company told the ABC that Abbot Point operators were confident they could manage floodwaters with new infrastructure, but were then overwhelmed by flows from neighbouring properties.

Adani's own testing showed water released into the wetlands on February 7 had almost double the authorised concentration of "suspended solids", which included coal sediment.

But Abbot Point Operations chief executive Dwayne Freeman said their testing showed the water with 58 milligrams of sediment per litre, and that this was not "coal-laden sludge".

"This is a very minor elevation in total suspended solids ... we are confident there will be no environmental impacts to the wetlands area, despite this unprecedented weather event," he said in a statement.

A spokesman for the Department of Environment and Science (DES) said it was awaiting test results on water samples taken by its own officers on February 8.

The Department of Environment and Science is awaiting water test results. ( Supplied )

The spokesman confirmed Adani's environmental authority for the port "imposes a maximum limit of 30 mg/L".

"DES will consider the results from the laboratory analysis along with other information in relation to the release event before making any determination as to whether or not the company has complied with the environmental authority conditions for the site," he said.

"Concurrent with the specific investigation into the release during the recent weather event, DES also continues to implement a long-term monitoring program in the adjacent Caley Valley wetland to determine whether any adverse impacts on environmental values is occurring."

'2017 release eight times over limit'

Adani is fighting a prosecution by the department over its 2017 release of coal-laden water from the port during Cyclone Debbie.

The department alleges Adani breached a temporary emissions licence (TEL) by dumping water with more than 800mg/L — eight times the authorised concentration of suspended solids.

A 2017 satellite image of Caley Valley wetlands (left) after water was released. ( Supplied: Queensland Government )

The department has not accused Adani of causing environmental harm from the 2017 releases, which passed through a monitoring point on the northern marine side of the terminal, adjacent to the Great Barrier Reef World Heritage area.

Three days before Adani's latest floodwater release, the ABC asked DES whether Adani had applied for a TEL.

A DES spokesman replied on February 5 that they were "monitoring the situation at the coal terminal with no flooding issues at present".

He said it had asked the port operators to "ensure that the site has taken measures and strategies are in place this wet season to manage and mitigate future impacts from operations during high-intensity rainfall events".

An Adani spokeswoman confirmed that "we did not apply for a Temporary Emissions Licence for the recent extreme weather event".

"We were confident that our improved infrastructure and processes at the terminal would be adequate to manage floodwaters," she said.

"However, because of the very high rainfall that has caused flooding and devastation across north Queensland, large volumes of floodwaters from surrounding properties entered the terminal site and exceeded the capacity of our water management system."

Abbot Point port and coal terminal is built alongside a vast coastal wetland. ( Supplied: Adani )

Mr Freeman said the port had released its test results "in an effort to keep the community informed and to demonstrate our commitment to operating transparently and with integrity".

"Normally a company would not release its test results, but we recognise there is a high level of public interest in Abbot Point Terminal's operations," he said.

Conservationists called on the Queensland Government to launch a second prosecution of Adani over Abbot Point.

Australian Marine Conservation Society campaigner Lissa Schindler said the company had "shown that it cannot be trusted with our precious reef".

She criticised Adani's advertising campaign designed to pressure the government into granting final approvals of its Carmichael coal project.

Ms Schindler said Adani instead "should have been ensuring its port was able to cope with Queensland's extreme weather events".

Mackay Conservation Group campaigner Peter McCallum said: "If you own and operate a port in Queensland on our precious Great Barrier Reef Marine Park, you must make sure it can withstand big storms."