Environmental regulators need to ensure water being discharged from the Hazelwood Pondage into the Latrobe River would not have long-term effects on the region's waterways, according to environmentalists.
Environment Victoria campaigns manager Nicholas Aberle was concerned PFAS levels in the pondage could have disastrous effects in year to come.
"PFAS could be the next asbestos. We won't find out the effects of these chemicals until further down the road, and until then, we should apply precautionary principles to manage exposure," Dr Aberle said.
"How confident are we that these levels are genuinely safe? What are the long-term effects of low-grade exposure to this chemical? We may not know for the next 20 years."
The Environment Protection Authority gave ENGIE permission to double the amount of water being discharged out of the pondage from 150 to 300 million litres a day if necessary, for up to 60 days.
ENGIE had applied for the emergency discharge licence to take pressure off the dam wall and reduce any risks associated with integrity issues in the 50 year-old structure.
The EPA issued a statement that PFAS levels were well below the 95 per cent level of protection ecosystem standard which was not unusual in many parts of the state.
The regulator said the additional flow would result in an increase in salt concentration but with no ecological impacts. Water turbidity and pH would also have negligible impacts on the river.
"I assume that ENGIE and the EPA will make sure that whatever water is being discharged, there will be no impacts downstream. Let's get the evidence there will be no impact," Dr Aberele said.
Dr Aberle was sceptical as to how ENGIE had allowed the dam wall to get to a state of emergency.
He was also concerned about the energy company's ability to manage a full-pit lake in the Hazelwood mine void.
"ENGIE has a big challenge in the rehabilitation of the mine pit and people need confidence. If ENGIE cannot look after a wall in a dam, how will they look after an entire pit of water?
"Why have pondage conditions become so frail that they need to have an emergency discharge? Why hasn't ENGIE been managing the wall for the past decade to ensure it is stable?"
An ENGIE spokesman said the company monitored water quality discharges from the pondage on a weekly basis as required by its EPA license.
"ENGIE Hazelwood continues to meet its regulatory obligations and is working with regulators, as required, on the final void rehabilitation," he said.