Restrictions are in place and urgent upgrades are planned for one of Melbourne’s largest dams.

An engineering report obtained by The Age suggests a dam failure in Melbourne’s Upper Yarra reservoir would result in flooding along the Yarra River, affecting tens of thousands of people and putting lives at risk.

The reservoir, located in the Yarra Ranges, can hold over 200 billion litres of water.

Work is planned for later this year to repair internal erosion and reconstruct the middle and upper levels of the towering embankment.

The engineering report says a spill could potentially claim hundreds of lives.

“The population at risk (defined as the population within the inundation zone in the event of dam breach) is in the range of 50,000 to 150,000 with most of these persons located within Melbourne and the inner suburbs,” a technical report by engineering consultancy AECOM said.

“The potential life loss is estimated to be in the range of 30 to 1000 … with those most at risk being located in the reaches upstream of Yarra Glen.”

Upgrades are not expected to be completed until mid-2021.

“When you have a report that warns of the potential loss of life of up to a thousand people, I would have thought the community deserved to be informed about that,” Shadow Water Minister Steph Ryan said.

“It's pretty worrying for people to wake up and read in the paper that there is the possibility of a dam wall failing that would inundate up to 150,000 people and result in potentially the loss of a thousand lives.”

That report commissioned by Melbourne Water and obtained by The Age says restrictions have been placed on the reservoir level to manage risk.

“There is no risk to public safety. Anyone who suggests otherwise is being incredibly irresponsible,” Water Minister Lisa Neville said. 

Ms Neville dismissed allegations that the document had been hidden saying that as a “tender document,” it was listed on the state government’s tender website.

“We have some of the highest standards in the world, if not the highest standards in the world,” Ms Neville said.

“This is business as usual for them, they assess their dams, they look at opportunities to fix any weaknesses and make sure our dams are the safest in the world.”