Populations of Western Australia's only freshwater aquatic mammal appear to be under threat, according to wildlife experts.

Although the rakali lives in patches across Australia, many people are not aware of the intelligent native rodent because of its elusive nature.

"They're really hard to spot, so that's part of the problem, especially here in Western Australia, they seem to more nocturnal than compared to over east," World Wildlife Federation Australia spokesperson Sabrina Trocini said.

To uncover more about the creature, Dr Trocini led a citizen scientist program to try find out where the animals live and where they are struggling.

In WA, the otter-like rakali is believed to have populations in the South West, Wheatbelt, and Kimberley regions as well as on islands off the Pilbara coast and isolated areas in Perth.

"We already knew that the rakali had declined in the Wheatbelt and our survey has ... actually confirmed that," Dr Trocini said.

"We had very few sightings in the Wheatbelt region."

Dr Trocini said the results from the three-month community survey in the southern half of WA suggested the animal was under threat in certain areas.

"We have a strong indication of localised declines," she said.

"Not only in the Wheatbelt but also in the Perth metropolitan area, especially around the Helena River catchment.

"We have found that there is a great number of historical sightings ... but we didn't receive any recent sightings."

Drying climate, illegal fishing may be to blame

Dr Trocini believes the drying climate is one factor triggering the decline in populations of the rodent.

"There's probably different causes, there's certainly the need for more monitoring and more studies," she said.

She said the main cause of mortality for the animals was getting caught and drowning in illegal freshwater marron traps.

"They shouldn't be used, because it's not just about water rats, fresh water turtles get caught as well," she said.

"So the best way and the legal way is to use group nets and drop nets for marron fishing."

Dr Trocini co-authored a report following the citizen science project, which was supported by the Department of Parks and Wildlife and a grant from Lotterywest.

She hopes the study will be the basis for further research to better understand the health of the elusive creature.

Dr Trocini said she hoped the community embraced the animal, which was often mistaken for a rat.

"It is a top predator of our freshwater ecosystem and we have to protect it," she said.

"I hope more people will know about our rakali in Western Australia and will start looking out for them and being a bit more aware that 'no it's not just a big rat, it's actually a beautiful native animal'."