At first light, agile wallabies make their way down to the river's edge.

[Didgeridoo music] Narrator: Mum and Bubba had it easy when the plains were full of green grass, but the dry season will test them.

If Mum doesn't get water, joey doesn't get milk.

But the river bank's a dangerous place.

Predators are watching.

[Calling] They have bubbas of their own to feed.

And Mum knows it.

She's been here before.

There's eyes in the sky, and there's something in the water.

An ancient predator honed by 200 million years of evolution... [Music] the saltwater crocodile-- the largest and most aggressive reptile on Earth.

♪ Narrator: Anyone who wants a drink... drinks from his river.

But for the wallabies, the sweet promise of fresh water is irresistible.

♪ Narrator: Salties are masters of stealth, and they can hold their breath for over an hour.

♪ ♪ Even little joey's on the lookout... and Mum doesn't waste any time.

The croc you can't see is the one you should be worried about.

♪ ♪ ♪ Narrator: The mob scatters in all directions... and panicked wallabies struggle to scale the crumbling cliffs.

♪ Narrator: One slip and it can all be over.