Travel: Western Australia wildlife sanctuary

You can have a cool, refreshing swim in the river today, no worries, mate. There's 6000 crocodiles in the 55km from the dam to Kununurra - that's one every 10m - but they're freshies so it's all good."

Boat skipper Dillon is full of reassurance as we launch into the murky depths of the Ord River beneath the massive Lake Argyle dam. This rammed-earth structure holds back Australia's largest man-made reservoir, Lake Argyle, nine times the size of Sydney Harbour.

Our aluminium cruise boat is soon picked up by a gentle current from the outflow of the Pacific Hydro private power station below the dam, which supplies power to Kununurra and the Argyle Diamond Mine nearby, the world's largest producer of white and pink diamonds.

We run downstream for only a minute before seeing our first freshwater crocodile sunning itself on a rock, its jaws wide open to let air circulate and cool its brain. Ultraviolet sunlight on a sweltering 35C day kills harmful bacteria in its mouth.

Although the freshies look as fearsome as their saltwater estuarine cousins, they don't regard humans as prey, preferring small aquatic animals, insects and fish. The man-made Ord River Scheme is a blessing for the freshies as they have a stable environment with no danger of nesting sites being flooded, so can grow a metre bigger than they would elsewhere.

Crocodiles have changed very little in their 200 million years of evolution, having survived the dinosaur extinction and the ice ages.

"They will continue to thrive long after humans have gone," Dillon tells us with a grin as if he is trying to brighten our day.

Our cruise boat has a canopy, which is just as well with the midday tropical sun blazing. The 450hp motor ensures we move along at a pace that generates good airflow. My sunhat is quickly removed before it's lost overboard. Dillon says the price to retrieve it is a carton of beer.

Great pied cormorants are common on the river and we watch one agile bird take a fish in its beak, throw it in the air, catch it head first and swallow it. Crocodiles take fish head first, too, otherwise the spines wedge in the throat, which causes drowning if they submerge.

Baobab trees are scattered along the riverbank in cute little family clusters. They are an intriguing feature of the landscape, their skeletal branches thrust out at strange angles like flailing windmills. These 100-year-old classic symbols of Kimberley appear to be bloated and bursting with water but the idea that they can be tapped for water is a myth.

There's no bird more fascinating and enigmatic than the orange-crested jacana, otherwise known as the Jesus bird or lily-trotter for its uncanny ability to walk on water plants. These multicoloured high-steppers spend their whole lives on the aquatic weeds, eating, sleeping and breeding. We see some new hatchlings, tiny balls of fluff, running across lily pads on their long, splayed toes. I try to dispel the unsettling thought of hungry crocodiles lying in wait on the riverbed below them.

We drift under large trees on the riverbank and listen to a cacophony from 10,000 flying foxes perched in the upper canopy. Actually black bats, these are fearsome-looking but harmless mammals with a complex social structure.

Dillon explains how the bats set up a nursery in one "creche" tree while the parents feed. They cover a 50km radius in their hunt while granny and grandpa bat stay home to babysit. The parents ignore all food within 3km of the home roost so that when they return at dawn, the old wrinklies can cover that ground without undue exertion.

No matter how clever and loving the bats are, millions of years of evolution have taught their sworn enemies to outwit them. To furtive, 6m-long olive pythons, bats are an endless smorgasbord lunch. Australia's largest raptors, the wedge-tail eagle and white-belly sea eagle, hunt for them in pairs; one bird stays in trees across the river from a bat roost while the other swoops into the colony. When a bat takes flight the eagle takes it on the wing.

Bats can drink only by swooping to the water and wetting their belly fur, which they lick. Freshies, also enemies, wait underwater with just their nostrils exposed and lunge when the bats dive.

We come to a wonderfully peaceful spot beside Spillway Creek where we eat lunch. Australian grebe feed on crustaceans in the weeds along the river and two jabirus prance about on the bank. A male pygmy goose lifts his head high to show off his shimmering bright blue and green neck. A white-breasted sea eagle circles overhead, watching for unwary freshwater turtles to surface. A pile of turtle shells under his eyrie attests to his skill in catching them.

Our journey ends at the Lake Kununurra diversion dam, a complex structure with 20 radial arm gates. These control the flow of the Ord River and gravity feed water into a system of irrigation channels that serves a vast area of fruit orchards and sandalwood plantations.

Ord River is a classic example of human intervention that has had a positive impact on a flood-prone basin. The resulting eco-system is completely stable and reliable and wildlife has increased tenfold.

From Kelly's Knob above the town of Kununurra I marvel at the scale of the Kimberley region - it's three times the size of New Zealand. The mind boggles but fond memories remain.

Paul Rush travelled to Kununurra courtesy of Air New Zealand and Tourism Western Australia.