Another seven companies are under investigation for releasing water at the height of the floods.
Rio Tinto Coal Australia said it has a good compliance history and comprehensive water management plans in place at all of its operations.
“The incident at Hail Creek Mine occurred following a heavy rainfall event and was the result of a failure in monitoring equipment,” a company spokesperson told ILN.
“Once this became apparent, we acted immediately to stop the release and water did not leave the mining lease boundary.
"This release did not meet our own high standards for environmental management and we have taken steps to prevent a repeat including replacing the faulty equipment, updating release procedures and equipment failure contingency plans, as well as working closely with the Department of Environment and Heritage Protection through its investigations.”
Queensland Resources Council chief executive Michael Roche has 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.
Roche said it did not appear the coal industry suffered as much damage as in the 2010-11 floods, but it was also clear that the legacy water issue from that time had not been eased because of the extreme rainfall recorded more recently.
All of the coal companies in Queensland are accustomed to dealing with tropical weather and after the 2010-11 floods had reinforced their flood defences, according to a research note by Paterson Securities.