The Environment Protection Authority is investigating whether Energy Australia Yallourn has breached the Environment Protection Act, following an ash slurry spill into the Morwell River.
But one community group has questioned why the spill was not made public until a month after the incident.
The EPA issued a statement on Thursday, saying ash slurry leaked into the river on 20 February when work on an ash line was carried out.
Ash is a by-product of burning coal to generate electricity.
A slurry of ash and water is carried from the power station to a storage site through a pipeline.
“Environment protection officers immediately attended and inspected the site, took samples of the spilled waste and have since launched an investigation into the incident,” the statement read.
“EnergyAustralia Yallourn committed to cleaning up and fixing the cause of the issue.
“A further inspection of the site by EPA on 5 March determined that the ash line was back in operation and clean-up activities complete.”
When asked how much slurry had been spilled, the EPA said the amount was part of the investigation and formed part of its initial enquiries of the operator.
The community group established in the wake of last year’s Hazelwood mine fire, Voices of the Valley, said “once again the community was not told what was happening at their back door”.
“The EPA now are trying to catch up with what was happening 30 days ago,” president Wendy Farmer said.
“It’s too late for safety precautions by the community.”
Ms Farmer said Energy Australia “did the responsible thing” by reporting the incident to the EPA.
However, she said the EPA should have notified the Department of Health, which should have issued a public warning.
When asked why the community was not made aware of the issue earlier, whether there were health concerns for the Valley community and whether the incident had been reported to the Department of Health, the EPA said in a statement, “when informed of a pollution event, EPA takes account of who is likely to be impacted and chooses the best channel to communicate directly with that community”.
“When matters become of wider interest, EPA issues statements through various channels.
“Material in the sludge, a mix of solids and fluids, is diluted by the Morwell and Latrobe River flows, but environmental and human health concerns were among our first considerations in response to the pollution.”
A Department of Health and Human Services spokesperson said the EPA confirmed with the Department on Friday that there was minimal risk from the event.
The EPA said it had received no reports of fish deaths in the river.
Environment Victoria healthy rivers campaign manager Juliet Le Feuvre described the Morwell River as “the most abused river in Victoria” due to multiple past diversions to accommodate mining.
She said the EPA should look at the whole impact of mining on the river.
In a statement, EnergyAustralia described the incident as “highly regrettable” and said it was working closely with the EPA to support the investigation.
“As part of our own internal investigations, we are looking at how we can improve both our operational management and maintenance practices and processes associated with the ash lines.
“We take our environmental responsibilities very seriously and will continue to work closely and assist the EPA regarding this incident.”