Nearby resident and environmentalist Julia Imrie said the clay thickening the water had been washed down from the Moolarben site, which had been cleared of its trees and topsoil, opening the clay in the subsoil to rain erosion.

Mrs Imrie said the situation was concerning for the river ecosystem, as clay embedded in the sand would increase algal growth and hurt the river fauna.

“The Moolarben Coal Operation was recently in the Land and Environmental Court over a similar incident last June,” Mrs Imrie said. “This is a significantly more serious pollution event.”

The clay-tinted water extended down the river beyond Wollar after three days, further than it had reached in June, and although it has since begun to clear, Mrs Imrie said yesterday it was still “pretty dirty”.

Although further measures were installed after the June incident, when Mrs Imrie said turbidity levels measured “off the scale”. She said the erosion control structures and dams intended to contain the sediment had proved inadequate after only a few days of moderate rain.

She said the state of the river after the rain made it difficult to believe the mine capable of redirecting creeks and controlling surface flow to protect the river as has been projected for stage two of the development.

She said environmental issues did not appear to be a priority for the mine’s management, which had no fear of being punished with a minor fine and the requirement to publish an apology.

She suspected this was the third breach of turbidity limits since June.

“The conditions are there, and every time they breach them, we’re going to make a fuss,” Mrs Imrie said.