With the bushfire season officially over, critical Mountains koalas have been returned to their habitat.

In December last year a dozen koalas considered critical to the future of the species were saved in a daring rescue by a local conservation organisation Science for Wildlife. As part of ongoing research under their Blue Mountains Koala Project, the team had found that koalas from the Blue Mountains Kanangra-Boyd National Park were considered critical to the survival of the koala species, due to their genetic diversity and the fact they're one of only two koala populations in NSW chlamydia free

With the support of the National Parks and Wildlife Service, Science for Wildlife saved eight adults and four joeys, taking them to Taronga Zoo for safekeeping (where local leaves were brought in to help the notorious picky eaters). The animals were facing certain danger from the Green Wattle Creek fire which had already burnt through 140,000 hectares and with more record high temperatures on the way.

Science for Wildlife executive director Dr Kellie Leigh said they had "been working in this area for many years now, tracking koalas to learn about them and assess their population numbers".

"We discovered the population of koalas in the Blue Mountains have high levels of genetic diversity. This makes this particular population very important for the survival of the species."

Due to the tall trees and rugged terrain, seeing the koalas for tourist purposes was generally not feasible but since 2015, the team had been finding and tracking individual koalas using koala detection dogs and mini radio-tags. It meant that as the wildfire threatened, Dr Leigh and the Science for Wildlife team and volunteers made the could quickly locate 12 koalas, and remove them until the crisis passed. Not all koalas were so lucky.

In the past few months Dr Leigh and others have been searching for wildlife that needs help, and putting in water stations and food drops until vegetation has recovered.

On March 23-25 the group was able to confirm the "great news" that the rescued koalas had been released back into the Black Range area. "Thirteen koalas including a bonus tiny joey in the pouch. They looked happy to be home," she said.

Dr Leigh said they had assessed the burnt area where the koalas were rescued to ensure that the Eucalpytus trees can support them again.

"Recent rains have helped and there is now plenty of new growth for them to eat, so the time is right. We will be radio-tracking them and keeping a close eye on them to make sure that they settle in okay."

San Diego Zoo Global has been a core partner in the koala project since it started and their long term support enabled the rescue and release. It will also support ongoing monitoring.

"Kellie and her team acted heroically, in the face of a mega-fire event, to save individual koalas who may be important to maintaining sustainable populations of the species in the future," said Dr Allison Alberts, chief conservation and research officer at San Diego Zoo Global.

Eighty per cent of the world heritage area burnt during the 2019 bushfires and there is now a long-term goal to recover the koala population in the region. It's estimated up to 10,000 koalas (a third of the total koala population of NSW) may have perished in the fires.

"Sadly, because NSW had over 100 fires burning at one time, with these fires it was a choice between protecting human life and property orwildlife. The national parks, which are normally refuges of safety for wildlife, had to be left to burn. We have to ensure that doesn't happen again," Dr Leigh said.

SDZG is a non-profit organisation working to fight extinction through conservation efforts for plants and animals worldwide. They have a fundraising campaign to support recovery of koalas, platypuses and other species at EndExtinction.org/Help. The campaign raised more than $500,000 in its launch week in January.