The NSW Environment Protection Authority is investigating a spill of coal waste and water from the Clarence Colliery mine near Lithgow into the Wollangambe River which flows into the Blue Mountains World Heritage area.
The Director of the Colong Foundation for Wilderness, Keith Muir, described the spill as a "real tragedy, equivalent to a giant oil spill".
The EPA learnt of the incident, believed to be the collapse of a coal waste dump, on Thursday morning, and coal material had affected at least 150 metres of the river, the EPA said.
"The cause of the incident is still being investigated but the EPA is obviously very concerned about any impacts on the Wollangambe River, which runs into the Greater Blue Mountains World Heritage Area approximately two kilometres downstream of the mine," EPA South director Gary Whytcross said. "This is a very sensitive environment."
The Clarence Colliery applied emergency protocols and shut down. The EPA was collecting evidence to determine potential breaches of environmental laws.
Mr Muir of the Colong Foundation said the collapse at the Clarence Colliery "will make the Wollangambe River turn black along entire reach and spread coal fines through the Wollangambe Canyons. These canyons are loved by many. It is a real tragedy, equivalent to a giant oil spill".
Greens mining spokesman Jeremy Buckingham said the coal industry was treating the environment "as their tip" and saw any fines it had to pay "as no more than the cost of doing business".
"The Clarence Colliery is a chronic environmental offender and, if there has been another toxic spill from this coal mine threatening the World Heritage-listed Wollangambe River, then the EPA needs to get serious by taking them to court where a significant fine can be imposed," Mr Buckingham said.
"This latest incident once again backs up the Greens' calls for coal mining to be banned in our water catchment areas."
- SMH, with Blue Mountains Gazette.