Australian Greens senator Larissa Walters said the option of letting mining companies dump discharge into rivers that flowed into the reef relied on the environmentally reckless and disproven theory that “dilution is a solution to pollution”

"Mining companies receive $11 billion annually in taxpayer subsidies – they should be expected to clean up their own mess,” she said.

"Safer disposal alternatives exist, such as reverse osmosis to purify the wastewater of salt and heavy metals.

"We also need renewed scrutiny of flood-event preparedness in the assessment of new mines, particularly as we can only expect more extreme weather events as climate change intensifies.”

Rio Tinto Coal Australia was fined $2200 last month by the Queensland Department of Environment and Heritage Protection for releasing water from its Hail Creek mine during February’s floods.

Another seven companies are under investigation for releasing water at the height of the floods.

RTCA said it had a good compliance history and comprehensive water management plans in place at all of its operations.

Queensland Resources Council chief executive officer Michael Roche rejected claims by some anti-coal activists that approved mine water discharges could be adding to flooding downstream.

“The amount of water being discharged by coal mines in the Fitzroy Basin is like adding a thimbleful of water to an Olympic swimming pool,” he said.