Hundreds of koalas have been killed by lethal injection in Australia due to an overpopulation crisis near the Great Ocean Road in Victoria.

The Australian reported 686 koalas were euthanasied in secret by wildlife authorities in three separate operations in 2013 and 2014. The culling project was kept under wraps due to fears of a community backlash.

Deakin University lecturer Desley Whisson, who specialises in koalas, clarified to Mashable it was not a secret cull but "a program implemented to reduce the suffering of starving koalas." She said despite reports, there was no effort to keep the program secret.

The koalas were captured by wildlife officials in public view before being sedated and put down. Healthy females were treated with fertility control hormone implants before being released into the wild, in an attempt to help with population control.

Koalas in the bushland habitat at Cape Otway are starving due to to the sheer numbers of the native animal and the decline of their food source — manna gum trees. Whisson says the numbers may have dwindled to 1000-2000 koalas in the region due to remaining gum trees being in poor condition.

"Koala over-browsing has caused drastic decline of woodland health and extent. In some areas the dieback is so severe that it has caused entire canopy death and koalas too are suffering," Cape Otway's Conservation Ecologyc Centre wrote on its website.

It highlighted solutions that were in place, such as planting 80,000 tree seedlings in the affected areas of woodland at Cape Otway.

State Environment Minister Lisa Neville has said it is a "complex and challenging" issue, which the government is trying to address in the most effective and humane way.

"It is clear it's an overpopulation issue and it is clear that we have had koalas suffer in that Cape Otway area because of ill health and starvation," she said, according to the ABC. "That's just not good enough and that's a terrible way to treat koalas.

"I'm wanting to make sure that we're taking the best action we can in this terrible situation of overpopulation. I don't want to see koalas suffer."

Whisson praised the government's action in the region, saying it was the only option for the koalas that were "passed saving." She said although many people suggested relocation, there is no suitable habitat not already populated and the move can cause the koalas more stress.

"Euthanasia of sick koalas is a humane action," Whisson said. "Anyone who witnessed the problem in 2013/14 would agree that it was necessary. It was great that the government responded in the way they did.

"A long-term management strategy that involves habitat (e.g. continued tree planting) and koala management (fertility control) is essential for addressing the ongoing problem though."

Frank Fotinas, who runs the local caravan park, said the koalas are good for attracting tourists but says they are totally destroying the environment.

"Koalas are great for business but if there's no trees, there's no koalas," he said. "A lot more were dying naturally than were euthanased. The whole of the cape smelled of dead koalas. It smelled like death."

Fotinas called for further government intervention to help solve the problem. Despite the cull in the area, koalas are continuing to overpopulate Cape Otway and the government continues to look into ways to manage this issue in the future.