Metals such as zinc, copper, nickel and aluminium, as well as elevated levels of arsenic, are much higher than healthy guidelines, and the contamination has seriously damaged the ecosystem of the river for 15 kilometres downstream from the mine, documents obtained by the Herald show. Environment groups have begun a civil court case against BHP Billiton, which operates the West Cliff coalmine near Campbelltown via a subsidiary company.

The Environment Minister, Robyn Parker, gave the Environment Protection Authority a stinging rebuke when she heard about the pollution yesterday.

''The EPA needs to lift their game,'' Ms Parker said. ''We've put them there, and given them increased powers and increased responsibility, and I need to see some action from them.''

Earlier yesterday, Ms Parker announced deep staff cuts at the Office of Environment and Heritage but had promised to strengthen the EPA significantly and to crack down on big polluters after last year's Orica scandal.

BHP Billiton received its court summons yesterday and did not respond directly to questions. But it sent a brief statement to the Herald, saying: ''The company complies with environmental regulations and is reviewing the details of this matter.''

A string of correspondence between the company and the EPA goes back as far as 2002, and shows that the regulator had been aware of discharges from the mine and some of its environmental impacts for most of that time.

The discharges from the mine flow into Brennans Creek, a tributary of the Georges River, and contain pollution from coal washing, water that has been pumped out of the mine tunnels, and stormwater runoff.

But the matter became public only because bushwalkers noticed the pollution and arranged for independent tests by Ian Wright, an environmental scientist at the University of Western Sydney.

About two years ago Dr Wright took a group of students and some rudimentary laboratory equipment to the river and has since returned many times to check and recheck the results.

''I thought 'it can't be as bad as it looks'. But I was wrong about that. You could just see the change in the water,'' Dr Wright said. ''It was grey coloured. There was a lot of turbidity and coal ash.''

The results showed startling differences from some of the pristine waterways nearby, on the edge of the Dharawal National Park. The aquatic invertebrates - mainly small insects - that form the basis of the food chain were either very scarce or missing altogether.

''It's knocking around the food chain and the biology in the Georges River,'' Dr Wright said.

''Upstream, we've got the full complement of invertebrates that you would expect to find. Downstream, there are groups missing and others at very low abundance. The invertebrate data is consistent with a very polluted or degraded waterway.''

The court case is brought by the National Parks Association and the Macarthur Bushwalkers Club.