The Queensland government gave gas companies permission to dump toxic water into the headwaters of the Murray Darling basin, in breach of environmental safety guidelines.
An ABC investigation has revealed the government granted approvals in June last year for the discharge of treated coal seam gas (CSG) water into the Condamine River south of Chinchilla.
That's despite the water - approved for release at a rate of up to eight Olympic swimming pools a day - containing 17 chemicals and heavy metals at levels considered toxic to animals, plants and micro-organisms that live in freshwater ecosystems.
Environment Minister Vicky Darling has promised to investigate the matter.
She said releasing CSG water into natural waterways was the least preferred option in Labor's CSG water management policy to be released on Thursday.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The ABC said the environment department approved the releases based on drinking water standards, not stricter aquatic ecosystem standards set by the Australian and New Zealand Environment Conservation Council (ANZECC).
Approval was granted to Origin Energy and ConocoPhillips and related to water from a desalination plant on the Walloons gas field, which is part of the companies' joint coal seam gas to liquefied natural gas (LNG) plant near Gladstone.
The companies have been discharging treated CSG water into the Condamine River since September last year, the ABC reported.
The Department of Environment and Resource Management (DERM) said it would amend the approval to ensure ANZECC guidelines were met in relation to the chemicals boron and cadmium.
The safe level of discharge for cadmium is 0.2 micrograms per litre, while the government allowed the company to release it at more than 10 times that level, the ABC said.
Ms Darling said she didn't want the burgeoning CSG industry to grow at the expense of landholders and the environment.
"That's why we are releasing a new policy which clearly sets the first priority - to reinject treated CSG water back into the natural coal seam," she said.
The revelations have angered the region's mayor, who said he was worried gas companies were not playing by the rules, and the government needed to better police their activities.
"Any release (of CSG water) into the riparian area or riverine ecosystems was to meet stringent environmental improvement guidelines," Western Downs Mayor Ray Brown told AAP.
"We were told they were under waste disposal standards which are much more strict than drinking water standards.
"Who has not followed this up? Whether it's the company or the state, is not acceptable to us. The standards are laid down in black and white."
