Environmentalists and traditional owners are complaining mining giant Energy Resources Australia (ERA) has failed to properly report a potential contamination leak in the heritage-listed Kakadu National Park.

The Environment Centre of the Northern Territory says a significant leak of sulphate detected outside the uranium lease in Kakadu last month is evidence of ongoing problems with the Ranger mine.

The head of the Environment Centre, Dr Stuart Blanch, says the information was leaked to his organisation.

"The supervising scientist did not report this information on its website," he said.

"It did provide it to a committee of interested folks, but this sort of information should be on its website.

"The information that it does have there completely masks and excludes the peak that shows that two times the reporting level of salt escaped from Ranger on around 10 April this year, but they did not report it."

For its part, ERA denies a spike in electrical conductivity represents any breach in the mine's operating conditions.

It says the mine remains one of the most highly regulated and scrutinised in the world.

But Dr Blanch said Ranger should be honest.

"They should have been on the phone to the Aboriginal community who are surrounding and living around this site and who are watching the operations," he said.

"They should have been on the phone to us and they should have made sure that it was reported.

"If they don't think it's a problem then they should be honest and open about it rather than waiting for people to leak it to us."

Justin O'Brien from the Gundjeihmi Corporation says it damages the historically good relations traditional owners have had with the company.

"We've seen this data, we know this took place, they know this took place," he said.

"They can't explain how it took place and the whole scenario is just patently inadequate."

But ERA spokesman David Patterson says that while there has been a spike it does not pose any significant environmental risk.

"We've observed, in the normal monitoring of water quality the creek, that there has been a spike in electrical conductivity," he said.

"It remains within the operating criteria for the mine. So there has been no breach of our operating conditions and we're investigating the source of that spike."

He says ERA may not be responsible.

"It's possible it could've come from somewhere else, it's possible it could have come from on our lease, and we're investigating that," he said.

Despite environmentalists' concerm, Mr Patterson says uranium could not have leaked from the site.

"The uranium levels are being monitored and are published and are publicly available and are available from the office of the supervising scientist and they don't confirm that hypothesis," he said.