Environment groups are calling for an independent inquiry into how flood damage at the Yallourn coal mine put Victoria's power supply at risk.

The groups have written to Premier Daniel Andrews asking for the probe, after the government declared a state energy emergency to expedite repairs.

In June, cracks appeared in the Morwell River diversion that runs through the mine following storms that caused floods in Gippsland and left parts of the state without power for weeks.

The diversion also collapsed after rainfall in 2012 which flooded the mine and shut down Yallourn power station for weeks.

Environment Victoria campaigns director Nick Aberle said questions needed to be answered about why the diversion had almost failed again.

"Our understanding is that it was rebuilt to withstand a one-in-1,000-year or one-in-10,000-year rain event," Dr Aberle said. 

Further flooding would risk supply

The Australian Energy Market Operator (AEMO) identified in its latest report into power reliability that further rainfall at Yallourn was the biggest risk to the nation's power supply this summer.

AEMO found it would take the plant 12 to 18 months to recover from significant flooding, leaving it out of action for the following two summers.

The Latrobe Valley community group Voices of the Valley co-signed the letter calling for an inquiry.

Its chair, Wendy Farmer, said she would like to see an inquiry similar to the one set up in the aftermath of the 2014 Hazelwood coal mine fire.

"We need to know that the people working at the mine are safe. This is actually a safety issue."

Decision handballed to regulator

Yallourn, a 1,480-megawatt (MW) brown-coal-fired power station, produces 22 per cent of Victoria's electricity.

In July, the state government gave the plant's owner, Energy Australia, permission to direct river flows around the diversion and into the nearby Latrobe River.

The government said the mine remained at risk from further rainfall and said water could also be pumped into the former Hazelwood mine in the event of heavy falls.

Energy Minister Lily D'Ambrosio said she was aware of the environment groups' request but there were no plans for an inquiry at the moment.

She said any decision about an inquiry would be up to the regulator, Earth Resources Regulation.

"What's important here is the fact that we've got some really strong processes in place to enable Energy Australia to undertake the works that they need to over the next 18 months to actually have a proper fix for the problem that occurred a few months ago."

Ongoing maintenance our focus: owner

Energy Australia said it would "fully cooperate and provide all relevant information" to support an independent inquiry if one was required. 

A company spokesperson said it had ongoing monitoring, maintenance and inspection at all its facilities to boost reliability and operated two batteries in Victoria.

"We also own Newport and Jeeralang power stations, representing around 950MW of capacity," they said. 

"The intermediate and peaking plants are generally brought into operation when demand is high, or as short-term replacements while other plants are serviced."