Mining company Vista Gold has been given the go-ahead to discharge water contaminated with toxic metals into the Edith River in the Northern Territory.
The company wants to reopen the Mount Todd mine, about 50 kilometres north of Katherine, but must first empty three retention ponds filled with water containing cadmium and copper.
It needs to empty the ponds in order to begin operations.
Under the discharge licence, Vista Gold will only be allowed to release water when the Edith River is flowing at a sufficient rate.
Territory Mining Minister Willem Westra Van Holthe says this will ensure the contaminated water is safely diluted.
"'I am satisfied that the work that is being done by Vista Gold, by the Environment Department, the EPA, and Mines and Energy, means that there will be little or no impact whatsoever on the Edith River," he said.
Mr Van Holthe says water in the river will continue to meet drinking water guidelines and the discharge will help reduce the risk of uncontrolled events.
"Either we leave water in situ and allow big rainfall events to cause uncontrolled discharges, which would cause enormous environmental harm, or we take charge of the matter and allow water to be put into the Edith River system in a controlled fashion that prevents environmental damage," he said.