Power generation at Yallourn has been cut again after heavy rain in Gippsland delayed mine repair work.
The power station that supplies about a quarter of Victoria's energy has 80 hours worth of coal available after flooding forced its mine to close for the second time this month.
This follows the collapse of a river diversion that damaged the coal conveyor system on June 6.
TRUenergy spokesman Carl Kitchen said power generation was now back to one of four units.
“One of the main conveyors was reinstated earlier this week, allowing the power station to generate electricity from two of its four units,” Mr Kitchen said.
The Australian Energy Market Operator has said it did not expect the reliability of electricity supply to be affected.
Recent rain, and increased flows along the Morwell River, has forced TRUenergy to shut down one of its coal conveyors.
Environment Victoria campaigns director Mark Wakeham said the problems at appeared to be much more serious than the company was letting on.
“The site seems to be inherently unstable and is currently flooding every time it rains,” Mr Wakeham said.
It comes as the Greens called for a parliamentary inquiry into the collapse of the Yallourn coal mine earlier this week.
A section of the diverted Morwell River collapsed on June 6, allowing water to pour into the open-cut mine.
The incident damaged coal conveyors, forcing Yallourn power station operator TRUenergy to reduce electricity output.
Greens leader Greg Barber said the Morwell River diversion ended up in disaster, despite receiving environmental approvals.
"We were told that this river diversion was designed for a one in 10,000 year flood event, and yet it ended up in disaster,'' Mr Barber said.
"This is a risk to the environment, to our energy supply, and in some cases, to workers' safety, and I think the Parliament should get into an inquiry about it.''
Environment Victoria campaigns director Mark Wakeham said the environmental impact of the incident was unknown.
"We are uncertain what the impacts will be on the Latrobe Rover downstream, and the Gippsland Lakes further downstream.''
Three of the four generators at Yallourn were expected to be operational by the end of this week, TRUenergy spokesman Carl Kitchen said.
Conveyor belts for coal were being repaired, and trucking of coal on public roads had now ceased.
A permanent repair to the Morwell River diversion was being designed, Mr Kitchen said.