Imagine being a baby turtle, newly hatched and ready to explore the big wide world — but being held prisoner in a small underground bunker.

Key points: Nearly half Australia's freshwater turtle species are in trouble

Nearly half Australia's freshwater turtle species are in trouble Foxes, roads, disrupted waterways, disease among the threats to turtles

Foxes, roads, disrupted waterways, disease among the threats to turtles The public can help scientists save turtles through a citizen science app.

According to one paper published in a recent special issue of the Australian Journal of Zoology, many hatchlings may die in the nest because lack of rain causes a hard cap of soil to form, which prevents them from digging their way out.

After analysing 10 years of data from nests in the La Trobe Valley in Victoria, the author concluded many hatchlings became fatal prisoners in nests constructed in hard clay soils.

And experts say drought could make the situation worse.

"Normally the hatchlings sit in the nest until the next time it rains and softens the soil enough for them to dig out," explained James Van Dyke, co-editor of the special issue of the journal.

"But if it doesn't rain sometimes they just get trapped.

"The soil on top of the nest gets baked and can be kind of like concrete if you go through a drought period and then hatchlings can't actually escape."

It's just one the many risks facing Australia's dwindling population of freshwater turtles.

It was once estimated there was up to 280 kilograms of freshwater turtles per hectare in the Murray River.

But since 1978, there has been a 91-per-cent drop in the numbers of the most widespread species Chelodina longicollis — also known as the eastern long-necked turtle or common snake-necked turtle — in certain parts of the Murray River.

This creature, sometimes called the common snake-necked turtle, is now no longer so common. ( Supplied: Ricky Spencer )

One of the major threats to freshwater turtles is the European red fox, which was introduced to Australia in 1845, said turtle ecologist Ricky Spencer from Western Sydney University.

Freshwater turtles lay their eggs on the banks of waterways, but these are often sniffed out and dug up by foxes.

According to Dr Spencer, in the Murray River 93 per cent of eggs are destroyed by foxes, and just one fox can do practically as much damage as a high population.

And foxes can also kill adult turtles.

Turtles are often the victims of roadkill as well, Dr Spencer said — especially on wide roads.

Another paper in the special issue of the Australian Journal of Zoology reports the eastern long-neck turtle is the most likely turtle species to end up as roadkill.

Watch out for turtles, especially when they're out on land looking for nesting sites. ( Supplied: TurtleSAT )

This is because it is so widespread across eastern Australia, Dr Spencer said, and because it walks quite long distances on land — especially during November, which is nesting time for most species of freshwater turtles.

That's why this crucial period has been dubbed "Turtle Month".

Scientists calling on citizens to help

This November, researchers struggling to come to grips with the scale of different threats to Australian freshwater turtles — and to find the best ways of protecting them — are enlisting the help of citizen scientists.

So, if you care about turtles and would like to help, you can download the TurtleSAT app and start mapping turtles and their nests.

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The idea is to photograph and report the location of any turtles, or signs of them — even if it's just a hole in the ground with egg shells scattered around.

"Alive or dead — if you see a turtle, put it in," said Dr Van Dyke, a turtle ecologist from the University of New South Wales.

Citizen scientists have already helped researchers work out where roadkill and fox predation hotspots are.

This is helping to prioritise the location of road signs, fences, and baiting programs to kill foxes.

Other threats to freshwater turtles include dams, drained swamps and wetlands, pollution, and disease.

For example, in 2015, Bellinger River snapping turtles (Myuchelys georgesi) were struck by a mystery disease that left them blind and starving.

While a virus is thought to have been involved, Dr Spencer said it was not clear why the outbreak occurred — what factors made the turtles susceptible to the disease.

If you see something like this, snap it and report it to TurtleSAT, as it could help identify where foxes are a threat. ( Supplied: TurtleSAT )

Turtles in waterways affected by salinity are also at risk of being infested by the Australian tubeworm, which encrusts turtle shells with calcium carbonate.

"It looks like a big concrete block," Dr Spencer said, adding the infestation had potentially killed thousands of animals.

Where have all the turtles gone?

The shelled body design of turtles is unique in evolution and they belong to a group of animals 200 million years old.

This group outlived the dinosaurs and yet now they are faced with mounting threats to their survival.

Globally, 61 per cent of turtles are threatened or already extinct. And in Australia, 11 of the 25 freshwater turtle species are listed as vulnerable or worse, by at least one state or federal agency and/or by the International Union for Conservation and Nature.

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Freshwater turtles play an important role in Australia's ecology, Dr Spencer said.

This includes being a major scavenger in waterways, eating everything from dead fish, insects and green algae to dead kangaroos or cattle that have fallen in the water.

"Freshwater turtles are the vacuum cleaners of the river," Dr Spencer said.

Without them, water quality and nutrient recycling would be at risk, he said.

Turtles have even been reported as living in raw sewage.

Freshwater turtles can live up to 75 years and because they eat so many things, they can accumulate pollutants like mercury and lead, Dr Van Dyke said.

"If there is any pollution in a system, they're going to pick it up," he said.

Dr Van Dyke has previously used blood and claw samples from turtles to measure pollutants in the environment in the United States, and he aims to set up a project to do this in Australia.

He said because the animals survive pollutants "pretty well", they can be good monitoring tools.