About 30 koalas have been euthanised after being found in poor condition at a Cape Bridgewater blue gum plantation.
The area has been reported as the most densely populated koala habitat plantation in south-west Victoria with some experts suggesting up to 500 koalas could have inhabited the area.
Chief conservation regulator Kate Gavens said the property was recently returned to the landowner after it had been stripped of blue gums in November.
A deer proof fence around the property, inhibited koalas from leaving from the site, is believed by the Department of Environment, Land, Water and Planning (DELWP) as contributing to the marsupials' current condition.
"Since Friday more than 80 koalas have been assessed and at least 30 euthanised due to poor condition," Ms Gavens said.
"The surviving koalas have been transported to wildlife carers for further treatment and rehabilitation.
"Wildlife welfare assessment and triage will continue this week with qualified carers and vets on site. The Conservation Regulator's major investigations team is leading the investigation into how this incident happened and who was responsible."
Portland resident Helen Oakley came across the bulldozed plantation on Wednesday.
After gaining access to the property from its manager, Ms Oakley along with her friend found multiple koalas who had died or were suffering.
"It's just devastation," she said.
"There has been complete bulldozing and clearing of the blue gums, vegetation and habitats. There were lots of koalas - to me they looked like babies - in the trees.
"This plantation was the most highly dense koala population on a blue gum plantation in south-west Victoria; now, where are they all?"
Ms Oakley is calling for legislation changes to protect the wildlife and avoid future devastation.
"The government has to come up with some sort of strategy if they're going to continue plantations," she said.
Keith Troeth, who cleared the plantation which his family owns, told The Age most of the koalas found dead on the land died of starvation.
He said a small number of koalas may may have died while the land was cleared with bulldozers last week.
"There may have been one or two koalas killed and I'll wear the responsibility, but it's not the big hoo-ha it's been made out to be."
All wildlife in Victoria is protected under the Wildlife Act 1975 which states the "killing, harassing or disturbing wildlife" can be penalised up to $8000 with an additional fine of more than $800 per head of wildlife.
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