MILLIONS of litres of radioactive water from the Ranger uranium mine have flowed into internationally acclaimed and World Heritage-listed wetlands in Kakadu National Park.

Traditional owners say they will oppose plans for a huge expansion of the 30-year-old mine by Energy Resources of Australia, unless the company upgrades outdated environmental protection procedures.

The Rio Tinto-owned ERA has tried to play down an alarming and unexplained spike in contamination in water flowing from the mine into Kakadu's Magela Creek between April 9 and 11, The Age can reveal.

 

About 40 Aborigines live downstream from a site where a measure probe recorded up to five times the warning level of electrical conductivity, which is a measure of contaminants including uranium, sulphate and radium.

Environmental group Environment Centre Northern Territory has been shown evidence showing the spike, which ERA representatives said had originated upstream from the mine and was not ERA's fault.

But, asked about the contamination, ERA admitted the source ''could not be determined and investigations are continuing''. ''It is possible that these have come from the Ranger operations,'' it said.

ERA's handling of the spike and other environmental concerns about the mine have strained its relations with the Gundjeihmi Aboriginal Corporation, which represents the Mirarr traditional owners.

In another unreported mishap at the mine, in December a poorly engineered dam collapsed, spilling 6 million litres of radioactive water into the Gulungul Creek, which flows into Kakadu.

Yvonne Margarula, a senior Mirarr elder, said the company tells her people ''only the good stuff … They don't tell us the whole story. [They] treat us mob like something else, like we don't know, like kids.'' She was worried that Aboriginal children swam and fished in the polluted creeks.

Justin O'Brien, the Gundjeihmi corporation's executive officer, said the traditional owners decided to make their concerns pubic despite having good relations with the company on other issues.

He said unless the company changes its environmental procedures, the Mirarr will not support any expansion of the mine - that includes a heap leaching plant, a tunnel under flood-plains, a 1000-person accommodation village, 650 evaporation ponds and a one-square-kilometre tailings dam.

The expansion, costing hundreds of millions of dollars, would extend the mine's operation to at least 2021.

The mine, 250 kilometres south-west of Darwin, has had more than 150 spills, leaks and licence breaches since it opened in 1981. ERA has been warned repeatedly about its management of the mine.

''We need the company to move beyond a culture of compliance into best environmental protection,'' Mr O'Brien said.

''In some respects, our relationship with the company has never been better, but for us to enter into genuine dialogue over the future of the mine the company needs to clean up its act on the environmental front,'' he said. ''Because of environmental issues, the entire relationship needs to be recast.''

David Paterson, ERA's general manager of external relations, said the company took the Mirarr people's concerns seriously.

He said ERA had regular transparent communications with the traditional owners and the Aboriginal representative organisation, the Northern Land Council.