Bleak outlook for platypuses in Vic river

A study looking for the elusive platypus in a Victorian river has found no trace of the much-loved duck-billed monotreme and says it is "functionally extinct".

Scientists say they've been unable to find a trace of any platypus in a Victorian river habitat. (AAP)

The platypus is "functionally extinct" in a Victorian river, with no trace of the elusive creature found in DNA testing of the water.

A study of the upper Wimmera River, near Ararat, filtered the water for platypus urine, poo, hair and skin to collect possible DNA samples.

The preliminary report, released this week, showed no trace of the platypus in an area which it had previously been spotted over the past two decades.

"There were surveys done in early 2000s and there were platypuses captured throughout that area but they've probably been in decline for quite some time," the study's senior ecologist Josh Griffiths from EnviroDNA told AAP on Wednesday.

"Now they seem to have disappeared from much of that catchment."

A lack of river flows, caused by irrigation and drought, is being blamed for the decline in population, leaving the river as a series of pools that slowly got smaller as the drought continued.

Mr Griffiths, who has spent the past decade studying the creature in Victoria, said any platypus still in the area could be isolated and living in farm dams.

"If you've got odd individuals scattered around the place, they're not going to interact, they're not going to breed, so in terms of a population it's functionally extinct," he said.

Playtpuses require several kilometres of river to live and will can only survive in an isolated pool for a limited time before the food supply runs out.

They will then try to move on, Mr Griffiths says, and if there's no river they will go over land, making them vulnerable to predators and dehydration.

Project Platypus, which monitors the species in the area, said a colony in McKenzie Creek, near Horsham, was the last hope for the much-loved duck-billed monotreme in the Wimmera.

"One of the biggest impediments (for that colony) is a barrier, a water measuring station, preventing them from going downstream," Project Platypus' John Pye said.

"What ends up happening is that the platypus become isolated above there, as to get below they have to walk along the banks ... which means they are vulnerable to predators."

The full report on the platypus DNA study will be published early next year.