Researchers undertaking a landmark study on the platypus are warning of significant population declines and localised extinctions across areas of South Australia and Victoria.

The study, which is still several years away from completion, seeks to establish a clear picture of the animal's population for the first time. Current estimates on population figures vary from 30,000 to 50,000 mature animals, according to the International Union for Conservation of Nature (IUCN).

The platypus is an Australian icon but landmark research being conducted by a large team of Australian scientists indicates the animal's future is under serious threat. Credit:Douglas Gimesy

"The platypus is notoriously difficult to study in the wild because it is a nocturnal animal and very elusive so there is no concrete population number," Richard Kingsford, Professor of Environmental Science at the University of NSW, told Fairfax Media.

"But what we have uncovered so far is leading us to believe that the situation for platypus right now in Australia is critical. We can report with certainty that they have disappeared from the Adelaide Hills, the Bass River and Avoca River catchments in Victoria and they have declined precipitously in the Wimmera River catchment in the Murray-Darling. Overall their population is in decline across the country."