A last-ditch attempt to save West Australian turtles in one of Perth's key wetlands is underway, after dozens of nesting females were eaten by foxes and squashed by vehicles.

Key points: There are grave fears for southwestern snake-necked turtles at Bibra Lake

There are grave fears for southwestern snake-necked turtles at Bibra Lake 15 pregnant turtles were crushed by cars last year and predators also pose a risk

15 pregnant turtles were crushed by cars last year and predators also pose a risk Turtle nesting refuges have now been installed between the road and lake

The southwestern snake-necked turtle — formerly known as the oblong turtle — is endemic to freshwater lakes in south-west WA.

In October last year, 15 pregnant turtles were found dead overnight on a stretch of road that runs metres from Bibra Lake, one of Perth's most significant wetlands.

Murdoch University environmental science PhD student Anthony Santoro said without quick intervention, road kill and hungry predators could soon wipe out the entire population at the lake.

Nesting turtles making a dash for a safe site were crushed by passing cars in October 2018. ( Supplied: Josie Parisse )

"I've caught about 500 turtles in here in the past year and only about 50 of them are female," he said.

"It's one female to every eight to ten males. That's not very good at all.

"In freshwater turtles you generally should expect an equal ratio of males to females.

"Essentially, if the predation and the mortality on the roads keeps happening, we're going to end up with no females and then basically the population will just die out."

Anthony Santoro has been studying the movements of turtles in Perth waterways. ( ABC News: Gian De Poloni )

Mr Santoro said infrastructure around Bibra Lake made it difficult for females to find a safe place to lay eggs.

"There's a wall that runs along the majority of the west side of the lake," he said.

"When the turtles would hit that wall, they then would follow it to the end.

"So basically, the wall was funnelling all of the turtles up onto this section of the road and that's where they were getting hit en masse."

All of the turtles found dead on the road adjacent to Bibra Lake were pregnant females. ( ABC News: Gian De Poloni )

Refuges installed to protect pregnant turtles

Keen not to see a repeat of last year, the local council has installed turtle nesting refuges in the sandy banks between the road and lake.

"We're hoping with the help of fences, it's going to intercept the female turtles before they cross the road," Mr Santoro said.

"They'll enter the cages, they'll lay their eggs in nests in there and then they'll be able to get out and get back into the wetland.

"The cage should then prevent predators like foxes, crows and magpies from accessing the nests and destroying the eggs, which allows us to get some babies back into the lake."

It's hoped nesting cages at Bibra Lake will stop turtles from crossing the road to breed. ( Supplied: City of Cockburn )

Mr Santoro said he found 135 nests dug up by foxes and birds during the 2018 nesting season.

"Based on how many turtles I've caught and tagged in the lake, that's probably most of — if not all of — the nests that you'd expect in this population," he said.

"Foxes are one of the main predators, they get both the adults and the nests.

"If all the nests are getting dug up, you're not getting any juveniles into the population.

"That is just further increasing the chances that this local population will end up extinct in the future."

This turtle nest was likely to have been dug up by a fox. ( Supplied: Friends of Queens Park Bushland )

Development blamed for 'putting turtles at risk'

City of Cockburn environmental officer Sophia Wright said last year's nesting season was a particularly bad for turtle deaths.

"The city was aware that there probably was an issue with turtle predation and turtle deaths from previous years, however only through Anthony's research have we realised the true extent of how serious this issue is and how many turtles we are losing every year," she said.

Sophia Wright says the City of Cockburn is boosting protection measures ahead of the nesting season. ( ABC News: Gian De Poloni )

"The main issue really is that we're allowing roads to be built so close to wetland environments where we are putting turtles and other native fauna at risk."

Ms Wright said the city was also planning a second annual feral animal eradiation program in the coming weeks and would look at installing a fauna underpass under the road in the long term.

Flashing signs warning drivers of the presence of turtles will also be switched on, while more cages are set to be installed before the start of nesting season in September.

Motorists on Progress Drive will be warned about the presence of turtles. ( ABC News: Gian De Poloni )

Mr Santoro said turtles were at risk of being wiped out at lakes across southern WA.

"The situation is a lot more dire than a lot of people realise," he said.

"This is likely to be happening at many other wetlands across Perth.

"If we don't do something now it's going to be too late. This turtle will essentially go extinct."

Editor's note July 30, 2019: An earlier version of this story referred to the turtles facing extinction. The southwestern snake-necked turtle is only under threat in certain areas, not as a species.