A major report to be released next week by WWF - the Living Planet Report 2018 - estimates koala populations are losing just over a fifth per decade with deforestation a major cause.

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"There is still a reasonable amount of genetic diversity left in NSW and Queensland and it's so important to maintain it for so many different reasons," she said.

The reasons include resistance to disease, particularly chlamydia, which affects almost all koala populations.

Koala populations in Sydney's south-west are a focus for conservationists, in part because of low-disease rates and their proximity to rapid urban sprawl.

Exposure to dogs and cats and other disruptions may trigger increased cases of chlamydia - since many animals carry the disease - from the added stress, Dr Johnson said.

Preserving connectivity across the landscape was important for the health of many species, especially koalas given the threats.

"We are isolating them on little islands," she said. "We really don't want that to happen to koalas."

Researchers are already detecting inbreeding issues in South Australia where animals were found to be suffering kidney problems and even misshapen skulls, affecting their ability to eat.

Election issue

Koalas are shaping up to be a prominent issue at March's state election in NSW.

The state government will spend $44.5 million on its Koala Strategy, "the biggest commitment by any state government to koalas", a spokesman for Environment Minister Gabrielle Upton said.

It is also committing $226,000 to research projects, including into chlamydia.

Labor said the government's plans included weakening land-clearing laws that removed protection on 99 per cent of koala habitat on private land, and had diluted its own Environment Minister's push to increase national parks.

"Saving our most iconic national animal will be a priority for a Labor government," Penny Sharpe, Labor's environment spokeswoman, said.

Dawn Walker, the Greens koala protection spokeswoman said her party's priority was "the immediate creation of a Great Koala National Park in the Coffs Harbour hinterland where 20 per cent of NSW’s wild koalas are found and are at ongoing risk from logging operations”.

Valentina Mella, a zoologist with Sydney University, said about two-thirds of the koalas in the Gunnedah region had chlamydia, which eventually leads to sterility and pain for the infected animals.

"We're still in the early stages of learning how to help," Dr Mella said, adding extensive efforts were needed, such as those used to save Tasmanian devils threatened by an infectious cancer. "It's exactly like the devils - it has to be 360 degrees."

Climate change poses another threat. Koalas are picky eaters, sourcing food from just 20 of the 600 eucalyptus species, but even then leaves must have at least 52 per cent water content.

"If there is less rainfall and higher temperatures [as modelled by global warming], it will impact on their feed," Dr Johnson said.