The owners of a gold mine in the Top End say they expect to begin releasing treated waste water into a river system in the new year.
A spokeswoman for the Northern Territory's Environment Protection Authority says miner Vista Gold will soon be issued with a new Waste Discharge Licence.
The tainted water was treated by adding about 1,000 tonnes of limestone to one of the Mount Todd mine pits.
Vista Gold chief executive Fred Ernest says the process will remove almost all of the aluminium, copper and iron in the water.
There may still be traces of manganese and cadmium in the discharged water, which will be diluted.
The licence will allow the company to release 11 gigalitres of treated waste water into the Edith River during the wet season.
Mr Ernest says treatment of the water began three weeks ago and it could be released early next year.
"The results are very encouraging," he said.
"We have seen an increase in the pH in the ...
top 40 metres of the pit.
"Things are progressing a little bit faster than what we had expected." The plan is part of a $6 million project to re-open the mine, about 200 kilometres south of Darwin, which closed 15 years ago.
The mine is predicted to hold about four million ounces of gold.