Plans to let more mines release excess water into Queensland rivers will pose a threat to the Great Barrier Reef, the Greens say.
Deputy Premier Jeff Seeney has told parliament he expects more mines to carry out the practice under a pilot program this wet season.
He says discharges will only proceed under strict environmental conditions.
Coal mines will have to show they're improving how they manage mine water, and invest in systems to minimise its generation and capture.
"They will have to make a substantial investment in this area to receive the benefits from increases in release opportunities," Mr Seeney said on Thursday.
"We will expect a number of coal mines will be able to demonstrate that they can meet these performance benchmarks."
Four coal mines in central Queensland were given permission to release legacy water into the Fitzroy and Isaac river catchments last wet season.
The expected expansion of the program has angered Greens Senator Larissa Waters.
"This is Campbell Newman putting our waterways at risk to save the big mining companies a few dollars," she said in a statement.
She said it was madness to allow waste water laden with salt and heavy metals to flow into waterways.
"With many of our rivers flowing into the Great Barrier Reef, the Newman government is also jeopardising water quality of this World Heritage Area," she said.
"The Newman government continues to ignore UNESCO's warning that the reef could be added to the list of World Heritage sites in danger within a year because it's being overrun by development."The state government says independent water monitoring from last wet season showed metal levels across the catchment were well below relevant water quality guidelines.