The Roper River.
Fed by underground springs, it flows throughout the year.
A vital refuge for a small mammal with an intense dislike for the sun.
The little red flying fox.
These bats are waiting for monsoon rains...
but now it's reached 38 degrees Celsius.
Just a few degrees more and they will die.
Squabbles break out for shade.
They are dehydrating.
Three hundred thousand bats are desperate for water.
Only the Roper River can save them.
By soaking their chests, they can collect a little water
to lick off back at the roost.
But this is probably the most dangerous thing they'll ever do.
Australian freshwater crocodiles.
Warmed by the summer heat, they are at their most alert.
A crocodile's jaws snap shut in the blink of an eye.
The bats' reactions...
must be quicker.
They must choose a spot and run the gauntlet.
The survivors will brave the river every day until the monsoon rains break.
Which must be soon.