A lack of research into platypus numbers is leaving the iconic mammal vulnerable to extinction, an expert has warned.

The platypus is predominantly found along the Great Dividing Range, in parts of Tasmania, across the eastern seaboard and in an isolated pocket of South Australia.

It can also be found close to major population centres such as in the Yarra River, just 10 kilometres from Melbourne's CBD.

In 2014 the International Union for Conservation of Nature (IUCN) raised the status of the platypus from least concerned to near-threatened.

But Centre for Environmental Stress and Adaptation Research (CESAR) senior ecologist Josh Griffiths said no-one really knew for sure how many platypuses there were in the wild.

"The problem is no-one's really looking," Mr Griffiths said.

"And that's one of the real issues with platypus conservation — there is no reliable way of estimating platypus numbers, even at a local scale.

"There's a number of areas where they're extremely vulnerable."

Getting accurate numbers is difficult

Mr Griffiths said studying the monotreme through traditional catch-and-release methods had proven ineffective.

"Partly because you don't catch many of them, but also once you have caught them they seem to avoid the nets, so it's very hard to catch them again, and it means you can't get an accurate estimate of numbers."

He said while he was fairly certain there were tens of thousands of platypuses in Australian waterways, the number could be as high as 100,000 or as low as 20,000.

"We don't know if there's half as many as there were 200 years ago, [or] a 10th of what there was 200 years ago. They could have increased for all we know," he said.

Researchers will now use DNA studies to track platypus numbers in the wild. ( Supplied: Gary Lewis )

What threatens platypus numbers?

Australian Platypus Conservancy biologist Geoff Williams said habitat destruction, climate change, predation and direct human contact were the main threats to the platypus.

This year, nine platypuses died in Victorian waterways after drowning in illegal enclosed yabby nets, the second-worst year since records began in 2010.

But Mr Williams said the actual number of deaths could be considerably higher.

"We suspect the number of deaths is just the absolute tip of the iceberg," he said.

"The vast majority of [platypus] mortalities do not get reported [because] most people are using them [the nets] illegally."

Mr Williams questioned figures from Victoria's Department of Environment, Land, Water and Planning estimating that only 5 per cent of platypus deaths were reported.

"The real number could be perhaps 1 per cent for all we know," he said.

"Consequently it's only if somebody accidentally discovers a net and has a look in it and finds a dead animal that we tend to get reports.

"The reason the numbers tend to be higher in Victoria probably doesn't reflect the fact the problem is any worse — it simply reflects the fact that Victoria has a better system for keeping track of these things."

An enormous illegal drum net was found on the banks of Gunbower Creek in northern Victoria, a hotspot for platypus deaths. ( Supplied: Swan Hill Fisheries Authority )

First national platypus DNA survey

CESAR has just launched a three-year national survey of platypus numbers in partnership with the University of Melbourne and the San Diego Zoo in the United States.

Mr Griffiths said the survey would take in Victoria and New South Wales, and move away from catch-and-release methods to a DNA sampling approach.

"We can now go and take water samples and look for traces of DNA," he said.

"And that enables us to do this large-scale research over about 1,000 sites … and that's never been able to be conducted before.

"It'll be looking at places where we know they used to be 20 or 50 years ago — are they still there now?"

Lack of rainfall is a major threat to the platypus. ( ABC Open: Simone Law )

What is being done to support platypus numbers?

In 1994, Project Platypus was established to act as an umbrella organisation for 11 Landcare groups in the upper Wimmera catchment to deliver large-scale environmental repair projects.

Project manager Allistair Stephens said while the project was not directly involved in counting platypus numbers, works were aimed at supporting a "healthy habitat for that sort of pinnacle species".

Mr Stephens said recent DNA testing of water in the Wimmera's upper catchment revealed there were no platypuses there, and he remained pessimistic about their future.

He said a lack of rainfall was a major threat to platypuses, who liked deep river pools with plenty of coverage and stable banks.

"We can do all that we can do to try and keep things trending in the right direction as far as improving habitat, but it's so dependent on rainfall, and there's not a heck of a lot we can do to improve that," Mr Stephens said.

Platypuses disappearing from entire waterways

Mr Griffiths said 20 to 30 years ago, platypuses were fairly widespread across western Victoria's Wimmera catchment.

But he said the millennium drought had resulted in the catchment's entire platypus population dying out, except for the McKenzie River, which received environmental flows.

"They've disappeared from the whole Wimmera River itself … and they've also disappeared from the lower part of the Murray Darling," he said.

"And it can't just be those areas where they're on a downward trajectory, but because they're not on any of the states' threatened species lists they don't get special consideration."