That all living creatures are, ultimately, spun from water and air by sunlight can be strangely less than clear in some of the world's most watery, sunny environments.

Take the Amazon: the food pyramid gets off to a cracking start - the world's biggest forest - but seems, on casual inspection, to stop there. To visitors hoping to see the stars of the wildlife documentaries, it can feel like a film set where everyone is on their tea break - apart from a few extras.

The problem is all that cover: it’s the perfect place to hide. So, while you don't quite have to go to the lengths of the wildlife paparazzi, camped up trees with telephotos the size of bazookas, it’s rare that anything much can be seen, close up, without patience, stealth and a good guide.

But there’s another watery region, bordering Amazonia, where the inhabitants are anything but reclusive - a Cannes of the natural world, except surprisingly few people know of it. Overshadowed by the Amazon's top billing, the Pantanal wetlands at the headwaters of the Rio Paraguai have become, by default, South America's best-kept wildlife secret. While Amazonia blows apart all pre-existing notions of natural scale, for close-up wildlife viewing the Pantanal wins hands-down.

A morning in August. The canopied launch glides across flat water, following the hieroglyphics of the narrow watercourse. The rain that poured off the surrounding high ground between November and April, flooding and fertilising all but scattered islands of this area half the size of France, has almost finished its slow ebb. The water and the life it supports is concentrated into a fraction of its former extent.

Rounding a bend, we are confronted by an image from prehistory, glistening black, motionless on the bank. In the Amazon, most caimanes spotted are at periscope depth, their heads appearing like waterlogged lumps of driftwood. But this one is blatantly sunbathing, and isn't about to give up a prime spot just because some tourists have turned up. As Tico takes us to within just a few feet, it pretends not to notice. Somebody asks if we can move back a bit - so it will all fit in the frame.

Thirty minutes later - having passed herons and hawks, kingfishers and more caimanes, magnificently double-chinned howler monkeys and a treetop-sprawling iguana - we nose into a steep grassy bank and climb ashore. Beyond the riverside levee the ground dips and turns muddy. At a level just above our heads all the tree-trunks change colour - off-white above, brown below - a graphic reminder of the region's double life.

But now it is our senses that are swamped, by a noise that appears almost to be inside our heads: a weird all-around whooshing and crashing that comes and goes in irregular pulses. Above us countless wood storks are trampolining in the treetops - and above them an air traffic controller's nightmare, the world’s biggest ever stack. Here and there the blur of black and white is punctuated by bright pink: the perfectly named roseate spoonbill. Vultures and caracaras skulk on the peripheries, ever alert to the chance of plundering a nest. Chicks that tumble and somehow evade these persecutors are not lucky for long. Others are also here for this seasonal delicacy. At first we see nothing in the dried-out lagoons bordering the nesting-area. Then, through dark windows in the wrack of water-hyacinth, alien shapes are seen.

Immobile and caked in mud, their darkly blotched bodies wound into arcane knots, anacondas pass the day in malevolent torpor.

Later we spot another in a shallow pool: an abstract mosaic of gold and black appearing through vivid green blanket-weed.

Lunch at the stilted lodge is fried steaks of pintado catfish - the seasonal fish bonanza feeds more than just caimanes and the multitudinous birds. Then, after resting through the hottest part of the day, we go to the small homestead where some local cowboys are waiting.

The horses are small but sturdy. From their backs we have an entirely new perspective. Away from the river and its thin gallery of woodland, the savannah stretches to an impossibly far horizon. The going is firm in places, waterlogged in others, above the horses' hocks. A group of cattle approaches, blankly curious. When the floods come, they and their keepers move out to higher ground.

With grazing compulsorily limited in this way, there is a remarkable coexistence between cattle and wildlife. Some distant white shapes the same height as the scattered cattle are revealed by binoculars to be giant birds: the jabiru stork, emblem of the Pantanal. The next day we pass a tree containing three structures like untidy coracles. On the rim of one, an adult jabiru stands to attention, its red collar brightly visible. Above the nest's parapet the heads of the chicks appear in occasional silhouette. Next morning it's downstream to a wide bayou off the main channel, to visit the giant otters.

There’s rustling inside a waterside tangle, then we notice a toothy, almost canine face observing us from the edge of floating water-hyacinth. Further up the backwater we hear an echoing, unearthly bark. "Jacare" says Tico: caiman.

In the afternoon we try a little of what everyone else is doing: fishing. Lumps of meat suspended beneath wire traces quickly bring piranha, their triangular teeth meshing with the precision of scissor blades. Then, at a patch of fast, broken water near a confluence, we tempt a handful of beautiful dourado, like gilded salmon. Near the other bank a dark shape emerges from the water and shakes itself like a dog: capybara, the world’s largest rodent. He ambles off, stage right - another of the cast who, after just three days, we feel we know almost personally.

Jeremy Wade, Wildlife Writer

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