Yolandi Vermaak knew the female joey was beyond saving when she could smell it.
"You could stand five metres away and smell that she's rotting, she's literally being eaten alive on the inside," Ms Vermaak said.
The Wombat Rescue manager said it was the worst case of mange she'd ever seen, forcing rangers to euthanise the joey on the spot on Saturday.
Ms Vermaak is calling for a national strategy to deal with the parasite and more resources and input from the ACT government, as well as trying to raise public awareness of the disease.
Mange is a skin disease caused by mites that has been running rampant in Australia's wombat population.
"There's this huge mange crisis. This is a national disaster but it's not really getting any traction or attention," Ms Vermaak said.
She received a call about the joey from a Gordon resident on Friday, who told her the joey was just standing in her garden.
When she saw the photo she knew it was too late. The joey's skin was crusty, with a bloody patch around its neck and its fur moulting off.
There's so many challenges that I'm facing. I'm treading water.Wombat Rescue manager Yolandi Vermaak
"That's what people struggle to understand. It's not just a skin condition; their organs start to fail, they have severe secondary infections," she said.
By the time she arrived it had escaped, but it was found nearby on Saturday in a paddock where a ranger euthanised it.
"It was so sick you could just walk up to her, she didn't try to get away," Ms Vermaak said.
Inspecting the body, she found the joey had been hit by a car and had a broken leg and gravel rash to show for it.
She said the joey would have been unable to sleep because of constantly scratching at the mange.
The body was destroyed so not to infect other animals who could feed on the body.
"It's like an atom bomb going off. This body filled with mites looking for a new host is being eaten," she said.
Treatment for mange in the wild is difficult. Conservationists use an automated flap on wombat burrows, which sprays the treatment fluid cydectin onto wombats' backs, Ms Vermaak said.
But there are difficulties - wombats tend to use multiple burrows, and other wombats or animals can trigger the flap.
In some cases Ms Vermaak has seen, sprayed wombats can also shake off all the cydectin.
Wombats with mange needed to be treated at least once a week for up to four to six months.
"There's so many challenges that I'm facing," she said.
"I'm treading water."
Ms Vermaak said a national strategy was needed to deal with wombat mange and to find a better and more efficient treatment. She said the ACT government could get involved too.
"I think what they (the ACT government) could do is help those that are doing that sort of thing," she said.
Ms Vermaak said more people needed to be aware of mange; when she posted the photo of the joey on Facebook a lot of people expressed surprise.
"Every time I post something like this, the frustrating thing for me is: 'I never knew that wombats get mange'," Ms Vermaak said.
"Now they all know and we can all put some additional pressure on the government."