Waterwatch regional facilitator Woo O'Reilly said sediment was running into the Molonglo River, smothering the platypus' food source, waterbugs.

"Where I've seen way too many examples of sediment being washed into rivers from development sites. I see that as a really direct threat to platypus," she said.

"In this part of the world, the feeling is they're still doing okay, but you've got areas like the Lower Molonglo ... [with development] potentially threatening the platypus populations down there.

"[So] we're not just resting on our laurels and assuming that they're doing fine. We're keeping an eye on things."

The species has been classified as "near threatened" in Australia since 2016, with the horror 2019 bushfires believed to have potentially further impacted numbers.

Ms O'Reilly said she wanted habitats to be protected before the species was labelled as "threatened", at which point it might be too late.

"By the time an animal or a plant is at a point where it's [threatened], it's harder to bring them back. Their critical mass is so greatly reduced, their resilience is so reduced," she said.

"If you're actually dealing with a species before, when you've actually got a chance of putting in interventions to improve numbers and improve resilience, you've got a better chance of keeping it that way, rather than letting it get to the brink.

ACT Environment Minister Rebecca Vassarotti said the government was committed to sustainable developments.

ANOTHER READ: Tangled lives: litterbugs put platypus survival at risk as entrapment numbers increase

"It is important that with the development that we do ... it is done is in an ecologically sensitive manner. And so there's an absolute commitment that that will happen," she said.

"There will always be circumstances where there are challenges and things might go wrong. And in that case, I think it's really important that we have compliance arrangements in place. And if there has been unintentional environmental damage, that we have the mechanisms in place to make sure that we can remediate those areas."

In an effort to monitor numbers, Waterwatch is running annual surveys during "Platypus month" - August - which requires volunteers to help spot the monotreme across Canberra.

The animals are more visible during August because they search further for food, and males start getting ready for breeding season in Spring.

ANOTHER READ: Platypuses have been removed from drying waterways in Tidbinbilla and taken to Taronga Zoo

There will be 34 one-hour surveys conducted at dawn and dusk across the region, with volunteers filling 300 spots over the month.

Catherine Czerw has volunteered for the program in the past six years.

She got involved after moving to Canberra from Western Australia, where there are no platypus outside of a zoo.

"I've subsequently moved to Queanbeyan, and that's a real hotspot for platypus. So you can see a platypus just walking across the footbridge. You know, they're just playing around," she said.

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