A dramatic claim that Australia's koala population is as low as 80,000 animals is looking increasingly shaky, with reports that the true population could be more than four times that figure.

But Australian Koala Foundation (AKF) chair Deborah Tabart is sticking with the figure, and says her organisation's estimates of the marsupial's numbers are more reliable than those of government agencies and scientists.

At issue is the AKF's claim koalas "may be functionally extinct in the entire landscape of Australia" and "there are no more than 80,000 in Australia".

Yet days after the AKF assertions were made, a South Australian government agency moved to give koalas in the Adelaide Hills district hormone shots to reduce fertility.

And the federal Department of Environment and Energy told 7NEWS.com.au that current estimates of the Australia-wide koala population were about 329,000 animals.

In some areas koala numbers are growing so quickly, fertility control measures have been introduced. Credit: Dave Hunt / AAP

'Vulnerable'

In NSW, environmental officials have rejected the AKF's "functionally extinct" assertion, but have said the animal is regarded as "vulnerable" in the state - which has a koala count of about 36,000.

"The NSW government doesn't accept this (AKF) claim, as there are many things we can do to improve the future of koalas in NSW," said a spokesperson for the NSW Office of Environment and Heritage.

Koalas are struggling in Queensland, too.

A Department of Environment and Science spokesperson said the government has recently appointed a Koala Expert Panel to develop strategies to boost the population.

Southern boom

But the story is very different in South Australia and Victoria, where koala numbers are booming - and where authorities are actually trying to reduce the animals' breeding.

On Friday, South Australia's Natural Resources, Adelaide and Mount Lofty Ranges agency announced a "fertility control program" across the Mt Lofty Ranges in the Adelaide Hills.

The agency's surveys show 150,000 koalas in the Hills and a further 50,000 on Kangaroo Island.

That does not include other koala population centres such as the Lower Eyre Peninsula, in the states' south-east, and in Riverland areas along the Murray River.

Population estimates

Natural Resources regional director Brenton Grear says the Mt Lofty Ranges population estimates are solid.

He said the surveys used a big network of community members recording koala locations, as well as targeted surveys conducted by agency staff and scientists, with the data examined by ecological modellers.

Chevron Right Icon 'We are pretty confident we have 150,000.'

"So it has been rigorously examined and we are pretty confident we have 150,000 of them," he told 7NEWS.com.au.

Grear said the population levels had led to "over-browsing" and there are simply too many koalas for available food sources in the area.

"One of the greatest threats to the koala population in parts of the Mt Lofty Ranges is the koala population itself," he said.

The agency is giving hormone implants to 200 koalas in a bid to reduce breeding.

A similar story is unfolding south-west of Melbourne where, across the sprawling Cape Otway region, koala numbers reached about 20 per hectare, prompting a cull of 700 animals in early 2014 because of widespread starvation.

It's thought that just one animal per hectare is a sustainable population level.

In 2015, contraceptives were implanted in 166 of the animals in a bid to get the population down and relocation of the animals is ongoing.

No backing down

But the AKF chair Deborah Tabart says there are problems with the way numbers are estimated, and rejects other scientific estimates.

"We get our figures through 30 years of science, we have 2000 field sites and 100,000 individually measured trees, and in the 128 federal electorates we have evaluated, we have determined how much habitat there is," she told 7NEWS.com.au.

Tabart said the numbers were being exaggerated to make the problem seem less pressing and because governments were protecting the logging and development industries.

She said many populations are also not viable because they are "inbred".

"I think what we see today is just a shadow of what was here," Tabart said.