The miner has been engaged in a clean-up of Camp Gully Creek, on the national park's southern boundary, after coal fines and sludge overflowed from the mine and into the creek in September.

Neither the Environment Protection Authority nor Peabody have been willing to give an estimate of how far the pollution had penetrated into the Royal.

The answer, pictures from former head ranger Bob Crombie show, is almost the entire length of the park.

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Mr Crombie witnessed the waters of Hacking River turned black in September as the pollution was washed downstream.

"I already knew it was there - I'd been there on September 7 and August 14 when the river was absolutely disgusting, so I wanted to see how far it went down the river," he said.

"I went all the way down to Audley [on September 16] and I found fresh coal on the picnic area at Wattle Forest and Ironbark Flat. There were schoolkids playing in the water at Figtree Flat and there were people actually sitting on chairs surrounded by coal waste at Ironbark Flat.

"I was pretty disturbed by what I saw.

"The river was pretty black and dark at Audley, there was coal waste in various places, and there was sludge in the pondage."

He informed rangers at Wattle Forest at the time.

"I was concerned very much about the health hazard of that water - I don't know if you've got black water running off the mine, whether it's safe. But you've got children playing in the water and old people having a picnic and no-one has told them so they can decide for themselves."

Camp Gully Creek feeds the Hacking River, which flows the length of the National Park.

The Mercury went to Red Cedar Flat last weekend and the creek was relatively clear after days of heavy rain - but bent plants on the creek bank showed it had been fully flushed out by the high water.

It remains unclear how far Peabody's cleanup will extend. Mr Crombie asked whether regulators were content for the rain and current to do that job.

"There's been a heck of a lot of rain ... I think the rain has done it for them," he said.

"The rain has removed it from Camp Gully Creek for them, but rather than to a specialist dump where [the miner] would take it, it's dumped it at Audley."

When asked last week, the EPA said its clean-up order extended just 1200m from the discharge point. The EPA would rely on the ecologist engaged by Peabody for further details.

This week the Mercury asked the EPA if it could confirm pollution as far as Audley. A statement in response did not address this.

"Metropolitan Collieries have [sic] been required to manage the clean-up of coal material in Camp Gully Creek and areas of the Hacking River," a spokeswoman said.

"The clean-up approach was prepared by an independent ecologist who carried out assessments in early September to determine the most appropriate methods.

"EPA officers have been routinely visiting and monitoring the site, as well as overseeing the progress of clean-up activities.

"If the EPA investigation finds any breaches, further regulatory action will be taken."

A Peabody spokeswoman would not comment on the extent of pollution.

"Peabody continues to fully cooperate with the Environmental Protection Agency as it conducts its investigation," she said.

"While the EPA's investigation is underway it would be inappropriate for the company to comment on 'estimated' impacts."

NSW National Parks and Wildlife (NPWS) referred the Mercury's questions to the EPA, saying it could not comment.

Problems with coal pollution here are not new. The Sutherland Shire Environment Centre's Catherine Reynolds said the group put in a nine page submission to NPWS about a pattern of similar recurring pollution events in August last year.