Crucial koala corridors are dwindling in Sydney's south-west, conservationists warn
Conservationists say koalas need to migrate between the Georges and Nepean river systems. (Supplied: Sydney Basin Koala Network)
In short:
Conservationists say six natural koala corridors linking the Georges River and Nepean River in south-west Sydney are at risk of being lost to development.
The New South Wales government says changes announced this year will protect more than 5,000 hectares of threatened native vegetation in the area.
What's next?
The koala group is calling for the formal establishment of a protected green belt connecting Sydney's major national parks.
When Martin the rescued koala was released in Sydney's west near Warragamba Dam, he trekked for 40 kilometres on his way back into the national park.
Martin's tracker showed him moving through Sydney's peri-urban fringe over four months, traversing tree lines and pockets of bushland in 2018.
Up-to-date aerial imagery shows that in 2025 Martin would have had to contend with cleared land and housing developments.
Before: Martin was tracked moving through forested areas near Warragamba Dam in 2018. . . After: New housing developments have cut off Martin's path. Supplied: Nearmap/Sydney Basin Koala Network. .
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Conservationists are concerned this is being repeated in Sydney's south-west in an area they say provides a crucial link for the endangered species between two of the city's major rivers.
Stephanie Carrick from the Sydney Basin Koala Network (SBKN) says housing projects are clearing migration paths for koalas, known as "koala corridors", at speed in Sydney's south-west and need to be halted.
"Once they [koalas] are somewhere and they can't move out and they can't meet other koalas, they just die out," Ms Carrick said.
"The problem with these big housing developments is that they create these houses that are so tightly rammed together that there's no opportunity for big trees.
"When they build them, they completely like moonscape the area."
Yellow areas suggest where corridors could be restored; green shows intact habitat and red where corridors are under threat. (Supplied: Sydney Basin Koala Network)
The SBKN has developed a map of all of the koala corridors in greater Sydney that connect up koala population centres in national parks.
Ms Carrick says it shows there are six important ones in the Campbelltown area between the Georges River and Nepean River that are under threat from housing developments.
The group is now calling for the formalisation of a legally protected Sydney koala green belt to guarantee the species' ability to migrate between the rivers and the ability to move all the way to populations in Sydney's north-west.
The SBKN says corridors like this one at Mallaty Creek are being eaten into by development. (Supplied: Sydney Basin Koala Network)
"They are going to have to meet other koalas and breed with other koalas to improve their overall health," Ms Carrick said.
"The koalas in South West Sydney are really healthy, but they have low genetic diversity."
In 2021 the NSW chief scientist recommended koala corridors in this area in Sydney's south-west be at least 390 metres wide, include buffers from human activity and be separate from bushfire asset protection zones.
Ms Carrick says many of the corridors have been eaten into by developers, but some would only need small amounts of restoration to become the perfect width to meet the chief scientist's recommendations.
A NSW government spokesperson said it had taken substantial steps to protect koalas along the Georges River in Sydney's south-west.
The government has been developing its own map identifying potential wildlife corridors to be protected in the area between the Georges and Nepean rivers.
Green indicates land to be avoided for development; red shows land for urban development and yellow indicates "excluded land". (Supplied: NSW government)
ABC Radio Sydney understands the finalised map will be exhibited with a ministerial direction early next year.
Earlier this year the government also announced it would be strengthening koala exclusion fencing guidelines as part of changes to the koala management plan in the area, known as the Cumberland Plain Conservation Plan, which was finalised by the former Liberal government in 2022.
"Under the enhancements to the Cumberland Plain Conservation Plan, 5,325 hectares of threatened native vegetation will be connected and restored," a spokesperson said.
In July this year, Planning Minister Paul Scully said the changes to the plan would balance conservation with urban development, which would support the delivery of 73,000 homes in the area.
Ms Carrick says the government's announced changes still allow for the most direct link between the rivers at Mallaty Creek to be cut off.
She also says in the meantime developers are trying to modify current proposals to incur into more than 50 hectares of conservation land.
Government securing national park and crossings
The network says it is also concerned about the number of koalas being killed on local roads.
Vehicles have struck 160 koalas in Sydney's south-west since July 2022, according to the SBKN's figures.
Ms Carrick is concerned this trend may increase with the development of Sydney's fringe in the Hawkesbury near Richmond and around Western Sydney Airport, which is due to open next year.
The state government has allocated $27 million to create koala-friendly crossings at Appin in Sydney's south-west, which include two underpasses and one crossing at a canal.
It has also provided grants to local councils to operate vehicle-activated warnings sites at known kill spots.
A state government spokesperson said it had been putting land aside for the new Warranmadhaa National Park along the Georges River.
"This year, 962 hectares of land was reserved as Warranmadhaa National Park, which will protect an important north-south koala corridor between Appin and Long Point," the spokesperson said.