A strangely shaped mountain catching the clouds high above the jungles of Venezuela.
Its summit rocks have been carved into a multitude of grotesque shapes.
The sculptor, an agent that is continuously at wor on much of the landscape of our planet: Rainwater.
It washes over the rock, eroding it chemically.
It permeates the cracks, freezes, and chips it off in flakes and splinters.
As the water flows downwards, it starts on a long journey
that will take it from the mountains to the sea,
and here, with a leap of over 3,000 feet, the highest made by any river,
it forms the Angel Falls.
Ourjourney begins not far from that towering waterfall
on the high moorlands of Peru, 15,000 feet above the sea.
Water is a very extraordinary and very precious substance,
the only one on earth, apart from mercury,
which remains liquid at normal temperatures and pressures,
so it's an essential part of the bodies of all living organisms, animals and plant.
Without it, life would come to an end.
But this particular water is a very rare kind.
97% of the water on earth is salty, the sea,
but this was distilled from the surface of the sea by the heat of the sun,
rose into the sky as vapour, condensed to form clouds and then fell again as rain and snow
to form streams of pure, fresh, sweet water.
But this particular stream is on its way to the sea a very long way away,
because these are the Andes, and this is one of the many streams
that can claim to be a source of the biggest river on earth, the Amazon.
The difficulties of living in this young and violent river are formidable.
Its waters are thick with powdered rock and mud, but they have gathered few nutrients,
and they rush down the valley at tremendous speed.
Anything that lives here has to be a prodigious swimmer.
And these are. They're torrent ducks.
They exploit the swirls and eddies with consummate skill,
paddling with strokes of their large webbed feet.
They head upstream, bracing themselves against rocks with their stiff quilled tail,
and using small horny spurs on the wrists of their wings to give them purchase.
A pair owns a stretch of the river, working their way up it to the frontier of their territory
when they abandon themselves to the flood and are swept downstream to begin again.
Anchored firmly to the rocks is a kind of moss.
Mosses are primitive, ancient plants that appeared on earth long before flowering plants.
This torrent moss is found in young rivers and streams all over the world,
and wherever it grows, whether in the Andes or here in Europe,
it provides shelter for a multitude of insect larv
In summer, these creatures are transformed and fly briefly above the river to mate,
but most of their lives are spent underwater.
Some are streamlined against the current.
The caddis fly larvae live in protective tubes, the hollow stem of a reed,
or a construction of bits of wood stuck together with silk.
Some weight themselves down by building their shelters from heavy grains of sand.
The larva of the blackfly holds on to a pebble with its back end,
while it grabs at food particles that are swept past it with the antennae on its head.
It grips the rock with a ring of hooks, but even if it loses its hold, all is not lost.
It has a lifeline of silk which it has attached to its chosen pebble.
Having hauled itself back, it now has to get a new grip.
It spins a tiny pad of silk from a spinneretjust beneath its mouth,
then it fixes its hooks into that.
The nets with which it collects its food are modified antennae,
and the larva brushes off what they catch with alternate flicks of its mouthparts.
Not all caddis larvae live in solid tubes.
This one builds a construction that serves both as a home and a food-gathering device.
It uses its silk to produce a funnel-shaped scaffold of criss-crossing threads.
Undulating its body is a way of aiding its breathing,
for the movement speeds the flow of oxygen-bearing water through the funnel.
It holds on with the hooks at the back...
...leaving its jaws and front legs free to do the construction work.
This blackfly larva wasn't saved by its lifeline.
But the caddis fly larva itself, ferocious and art trapper though it is, is also at risk.
The dipper relishes it.
Dippers live both in the rivers of North America and Europe.
Underwater, their swimming technique is quite different from the torrent ducks'.
Its feet are not webbed like a duck's, so it propels itself with its wings, flying underwate
In similar cold, fast-flowing streams in North America
lives a kind of giant newt, the hellbender.
When it's young, it also, like a dipper, takes insect larvae,
but it can grow to over two feet long, and then it seeks much bigger prey.
A crayfish would suit it admirably.
A narrow escape. The crayfish saved itself at the last moment by a convulsive snap of its tail,
but the hellbender doesn't give up easily.
Both animals try to keep out of the current and habitually creep into crevices.
But that sometimes is a mistake.
Streams that tumble down the sides of the valleys and feed young rivers
have their own population.
In Malaysia, the big-headed turtle clambers around the waterfalls, using its tail as a prop.
In West African waterfalls, and nowhere else, lives the extraordinary hairy frog.
Its so-called hairs are filaments of skin on its flanks which act as gills,
helping it to absorb oxygen from the water.
And, almost as unusual, it has claws that help it grip the slippery stones
The many sources of the Amazon began as rivulets on the eastern flanks of the Andes.
Now, 5,000 feet lower down, each has grown beyond recognition and cut its own zigzag valley.
White water, tumbling down the valley wall, joins the brown water of a larger tributary,
heavy with mud and sediment.
And as it gets bigger and bigger, so it becomes more and more powerful.
It's the dry season at the moment and the river is comparatively low.
But during the rains, when it's in spate, its waters rise up over here
and the sheer volume and weight and force of them can shift boulders the size of these.
The volume and speed of its waters are not the river's only weapons.
It also has teeth.
And in this empty rainy-season part of its bed, you can see them.
Sand and gravel, fragments of rock that have been eroded from higher up in its course
and which the river hurls with enormous force at the rocks of its river bed.
With such tools, it can carve away the sides of mountains.
Young, vigorous rivers transform the land, demolishing the mountains,
breaking down the debris into smaller particles and carrying them away downstream.
This river in China is perpetually so turbid that it's called the Huang Ho, the Yellow River.
It carries a bigger load of sediment than any river in the world.
During floods, each cubic yard of water contains over 2,000 pounds of soil and pulverised rock.
Rivers in the full vigour of their youth are terrifyingly strong.
They roll great boulders along their beds,
they cut away at the banks, undermining trees which crash into the waters and are swept away.
When a river encounters a band of unusually hard rock, such as an ancient flow of basalt lava,
its progress is temporarily slowed.
It spreads out across the barrier and then tumbles over the front edge.
So are formed some of the loveliest cascades.
These are the falls of Iguacu on the border of Brazil and Paraguay.
They can't compare in height with the Angel Falls,
but in terms of the volume of water that passes over them, they are incomparably bigger.
The falling waters pound away at the base of the falls,
undercutting the basalt until blocks split off the face.
So the falls steadily work their way upriver, leaving downstream a deep gorge,
and animals live even here, within the falls themselves.
Swifts perch on the rock face behind the cascade.
Every evening they congregate high above Iguacu.
After a day of hawking for insects, they're ready to roost.
And where safer than behind a screen of falling water?
Some dive down with such speed that they shoot right through the fall.
And now the river has left the mountains far behind
and has changed its character considerably.
It's bigger, it's broader, and its waters carry not only sand and gravel
but rich nutrients washed in from its vegetation-covered banks.
And after it's gone over its last rapids and tumbled over its last fall,
it becomes a very different river indeed.
It's middle-aged: Ampler, less violent, more sluggish and richer.
On the banks of the Amazon tributaries, the jungle stands thick.
Birds like the sun bittern stalk quietly in search of a meal.
Huge fish cruise through the slow waters.
The arapaima, one of the largest of freshwater fish, grows over six feet long.
The Amazon contains over 3,000 different kinds of fish. That's more than live in all the Atlantic
Rays almost certainly evolved in the sea,
but this species has managed to make the change to fresh water and lives high up the Amazon.
Many fish have evolved here in fresh water
and become suited to all its variations of depth, speed and chemical composition,
to muddy water and to clear, to stretches that are thick with plants and places where there are none.
Their variety is enormous.
Take, for example, just one family: The catfish.
They're bottom-dwelling fish, with feelers on their snouts that have sense organs on them,
so the fish can feel and taste their way through the thick, muddy water or at night.
There are small ones and immense ones,
some that give electric shocks and others that swim upside down.
Those in fast-flowing waters
have suckers on their chins or undersides with which they cling to rocks.
In South America alone, there are 1,200 different species of catfish.
In these crowded waters, many fish give special protection to their young
for the first few weeks of their lives.
This fish, the discus, goes even further.
It provides its fry with special food.
The parents exude a nutritious slime from their skin
and the young graze over their flanks, feeding on it.
After a week, they're big enough to feed on small particles floating in the water.
These are now a month old and have already assumed the disc-like shape of their parents.
They're becoming independent, but they've strayed past the lair of an electric e
The eel has poor eyesight,
but it detects the presence of objects around it with short electric discharges, a kind of radar.
It rises for a gulp of air. This time the young discus seem to have escaped detection.
But the eel can also produce a major electric shock which stuns its prey.
It releases its capture. Perhaps so small a fish is not worth eating.
The young discus, apart from the marks of the eel's jaws on its flanks, seems no worse off.
One Amazonian fish puts its eggs beyond the reach of any water-living predator:
On leaves overhanging a river.
A pair of splashing tetras are courting.
They curve their bodies and, for an instant, leap clear of the water.
Sometimes a third fish joins in.
The bigger of the two is the male.
For a moment the pair hang on the leaf, supported by the suction of the male's floppy fins
Again and again, they jump. In this one moment, the female lays her eggs and drops off,
and the male fertilises them and follows her.
Each time, they leave behind a dozen or so eggs.
A few infertile eggs drop off, but they're not wasted.
Eventually as many as 200 eggs are safely placed out of harm's way,
and the river can be an exceedingly dangerous place.
Piranha, the most savage of all the Amazon's fish.
A swimming capybara suddenly realises their presence and tries to retreat, but it's too late.
The splashing, the taste of blood spreading through the water,
attracts more of the shoal until there are hundreds, all possessed by a frenzy for flesh.
None are much more than a foot long, but their teeth are sharp enough to cut clean through bone.
Within minutes, there's little left.
As the river gets older, it slows down. A minor obstacle in its path is now enough to deflect it.
The water flowing round the outside of a bend speeds up and cuts away at the bank.
On the inside, where the current is slow,
the water drops its load of sediment to form a shoal.
So the bend becomes more exaggerated as the elderly river swings from side to side
in a series of loops and meanders.
One bend may approach another until the neck of land between them is so narrow it collapses.
Then the river takes the shorter course and the meander is left isolated as a curving lake
There the water, at last, is still.
Plants no longer have to fight against a current, and the lakes become clogged with vegetation.
These are the largest floating leaves of all, the leaves of the famous giant Amazon lily.
Covering the water with leaves of this size is very aggressive,
for it cuts out the light below, making it difficult for other plants to grow there
The upturned rims of the great pads, as they grow, thrust to one side all other floating plants
To prevent these leaves being destroyed by being eaten by fish,
they are protected with very effective and ferocious spines underneath,
as you can see most clearly on this half-opened bud.
It can develop from the size of a soup plate to a huge emerald disc six feet across in a few days,
growing at a rate of one square inch a minute.
The flowers grow with similar speed.
Each opens first in the evening and remains with its petals spread and fragrant all night.
By the morning, however, it's closed again. But during the night it's taken prisoners.
Inside the flower are beetles.
Sometimes there are as many as 40 of them in a single bloom.
They're not there just by accident. They've been attracted by sugary outgrowths in the centre.
While they're trapped in there, they will feed on those.
This evening the flower will open again, the beetles will be released
and they'll fly off carrying pollen to cross-pollinate another lily flower.
And then, afterjust two nights, this bloom, by now turned purple, will crumple and die.
The leaves, strengthened by air-filled ribs beneath, can support the weight of a small child,
and water birds can walk over them with complete confidence and safety.
The jacana has greatly elongated toes that can spread its weight so effectively
that it can tread on very flimsy leaves without submerging them.
It seeks insects, and there are plenty to choose from.
The pond skater sits on a leaf, but it could sit on the water,
for the surface forms a platform that supports many small creatures.
Water molecules are bound by a force akin to magnetism.
They're not attracted to molecules of air above, so their forces are concentrated sideways,
giving the surface a specially strong tension, and the pond skater hunts on it.
It's lost its prey under the leaf.
This time there is no escape. The pond skater stabs its victim and sucks it dry.
It's crucially important for the pond skater to keep meticulously clean.
The waxy surface of its body and the hairs on its feet repel water,
but any dirt on them that is wettable would break the surface-tension film.
They're aggressive insects, each with its own territory among the lily pads.
Intruders are immediately chased away, and fights between rivals are common.
The surface-tension film is not only the pond skaters' platform, but their sounding board.
Through sense organs on their feet, they detect vibrations caused by the struggles of an insect,
and by bouncing up and down they communicate,
sending keep-out signals to rivals and come-hither signals to potential mates.
Whirligig beetles use vibrations of the surface fi in a different way.
They create ripples, and by monitoring the returning echoes,
they detect the presence of other creatures and obstacles around them.
They have excellent eyes, partitioned so that the lower half peers down
to see what's happening in the water beneath.
Hanging from below the surface is another hunter.
Its tail has two tubes which penetrate the surface film and collect air so that it can breathe.
At its other end, its head has ferocious jaws with which it seizes its prey.
This is the larva of the giant diving beetle, and it's caught a tadpole.
It has to come to the surface, even when it's adult, so it can collect air
to sustain it on its hunting forays down into deeper waters.
The water boatman patrols the surface not from above, like the pond skater, but from below.
The two kinds of insects manage to collect most of the creatures trapped in the surface film.
The camphor beetle lives on plants at the water's edge,
but it is perhaps the most versatile of all water-walkers.
It can run over water, like a pond skater.
It can also produce a substance which reduces the tension between water molecules.
In emergencies it squirts this from its tail, and with the tension pulling hard at the front,
it shoots across the surface so fast that the only way to see it clearly is in slow motion.
And, as a final demonstration of its versatility, it can, like most good beetles, fly.
One particularly ferocious hunter lives on the edge of lakes and ponds in Europe,
the fishing spider.
It uses the surface-tension film in the same way as other spiders use their webs.
With its front legs resting delicately on the surface, it feels for tell-tale vibrations.
But it also has excellent sight and can see potential prey below the surface.
The stickleback sees only the spider's feet.
That is a greatly slowed-down version of the kill.
In reality, the pounce is rapier-swift
and the stickleback had little chance once it strayed within range.
The lakes and ponds fed by streams or cut off from the main river are comparatively small.
But where rivers flow into basins created by geological faults,
their water accumulates in immense lakes.
This is Lake Prespa in Yugoslavia. Not the largest of lakes but, even so, 20 miles long.
As the rivers enter its still waters, they lose their impetus and drop their sediment,
so such lakes are potentially fertile, and their animal inhabitants,
no longer harassed by a current nor hemmed in by a shallow bottom or banks,
can proliferate, and they do.
Fish swarm in their waters.
And fish-eating birds, like pelicans and cormorants, swarm correspondingly.
Land-based creatures haunt its margins.
These may be its most fertile parts, for the lack of strong currents in a deep lake
can leave the bottom starved of oxygen,
but in the shallows, especially when warmed by the sun, algae and other plants flourish,
small invertebrates proliferate and there's food for even the least agile of hunters.
But in one way these large lakes are very special.
This trout, with distinctive red spots, lives in Lake Ohrid,
a few miles away from Lake Prespa, but nowhere else in the world.
Isolated in the lake, communities of fish become very inbred.
Small characteristics that could be lost become fixed, and the fish evolve into new species.
A similar thing has happened to the shrimps.
And among the many different species of water snails, several are now unique to Lake Ohrid.
In the heart of Russia lies a stretch of fresh wat so huge and so ancient
that these processes have produced new species on a scale unequalled anywhere else in the world,
Lake Baikal.
The lake lies in a great depression formed by faulting in the earth's crust.
It's 400 miles long and 5,000 feet deep, the deepest of all lakes.
In the depths of the lake, 1,000 feet down, lives a unique kind of salmon, the omul.
In summer, they move up into the shallows and feed on caddis fly larvae and sand hoppers,
and here they're caught in great numbers for their delicious eating.
But this is only one of Baikal's special inhabitan
Of the 1,200 different kinds of fish and other animals and 500 plants that it contains,
over 80% are unique.
There are unique molluscs, unique flatworms and even one unique mammal, the Baikal seal.
This tiny seal is almost certainly descended from the ringed seal of the Arctic Sea.
Today the lake is over 1,000 miles away from that sea.
It's likely that their ancestors arrived during the Ice Age,
when the journey may have been shorter and easier.
Since then, cut off from other ringed seals, they've developed in their own way.
The Amazon has no great lake on its course,
so even in its middle stretches it still carries mud from the Andes.
The Rio Negro, which joins it, is clear,
for it has come from the north-west where the rocks are hard and bare.
The two immense rivers flow for miles alongside one another in the same bed, scarcely mixing.
As well as sediment, they also carry abundant nutrients,
and life on their banks flourishes as never before
Herds of capybara wade through the shallows, cropping the luxuriant plants.
They're excellent swimmers, with webs between their toes,
and they have that placing of eyes, ears and nostrils so valuable to mammals that swim,
on top of the head, so as the animal lies submerged,
they can see, hear and smell what's going on above water around them.
Giant otters have a similar head design
and sometimes lift themselves above the surface to get an even better view of their surroundings.
This Amazonian species is the biggest of all otters, six feet long and a powerful swimmer.
It's well-equipped with large, webbed feet, a flattened tail and sensitive whiskers.
A pair lays claim to a stretch of river by making patches on the bank,
marking them with their own personal smell.
There are otters in many of the great rivers of th world and they are the most graceful of swimmers.
In India they share the harvest of fish with the gavial.
Most of the crocodile family, when adult, feed largely on carrion,
but the gavial eats only fish, and has long, narrow jaws, studded with abundant teeth,
with which it catches them underwater.
A host of birds also claim a share of the river fi
This is the hooded merganser, one of a group of ducks called sawbills.
Its beak, like the gavial's jaws, is long and narr so it's easily snapped together underwater,
and it also has a notched edge to give it a grip on the slippery fish.
But their feathers trap so much air that the pair have to work very hard to get down to any depths.
Coming up again is easy enough.
But the meal was a mere mouthful, and the merganser must look for another one.
And on the bottom lurks more danger for a fish.
A worm, perhaps?
No, the deceiving tongue of a turtle.
And in the sky above the river, more trouble for a fish.
The kingfisher.
And there's still one left for next time.
The fish eagle is not a diver but a pouncer, with a marvellously coordinated action.
The aerial onslaught on the fish continues not only throughout the day but at night.
An owl goes fishing in Africa.
Its legs are bare. Feathers would drag in the water.
And it has spines on the underside of its toes which give it a firm grasp on a fish.
In the last phase of their lives, these great rivers often flow out of control.
Their tributaries in the mountains, fed by the heavy storms of the rainy season,
pour so much water into them that they burst their banks.
The Amazon rises every year to flood tens of thousands of square miles of forest,
in some parts as much as 40 feet deep.
Some of these trees are flooded for eight to ten months every year.
They need only a few months annually out of water for them to grow
and for their seeds to sprout.
We still don't know exactly how they manage it.
As the floods well out over the land, fish from the river travel with them.
This is going to be their best feeding time in the whole year.
And so it is for other creatures too.
Among the fallen tree leaves that carpet the bottom lies the mata-mata turtle,
marvellously camouflaged, waiting for a decent-size fish.
And there are plenty already here, sheltering, like the turtle, among the still unrotted leaves.
Piranha are here too. These are not the flesh-eating kind.
Their teeth are used for something different: Frui
As the river becomes older and older, its riches increase still further.
All over the world as rivers approach their end, they begin to deposit the sand and mud
that they've gathered from so far and carried for so long.
In many parts of the world reeds grow thickly on these shoals and banks,
and their stems collect even more sediment as the river waters swirl through them.
Living in these dense reed beds requires considerable skill.
The little bittern is able to find its nest
hidden out of sight somewhere in this seemingly uniform stretch of reeds.
It regurgitates from its crop ample supplies of fish and frogs for its young.
Their world is an infinity of vertical stems, but they're nimble climbers from an early age,
and they leave the nest within a few days of hatching.
There they wait, almost invisible, for their parents to return with restocked crops.
The reed-clogged waters of a river delta are full of potential riches,
not only for birds but for human beings.
The reeds themselves are used for many purposes, but it's not an easy life here.
Firm land on which to live is hard to find.
In the Danube delta, the few solid sandbanks are tightly packed with dwellings.
Earth has to be conserved with piles to prevent a slight change in the current washing it away.
And there's the threat of a rise in the water leve caused not only by rainstorms upstream
but an unusually high tide, backed by a storm sweeping up from the sea,
which can cause devastating floods.
In the twin joined deltas of the Tigris and Euphrates in Iraq,
the marsh Arabs have become specialists in an amphibian life.
Their houses seem to have solid enough foundations.
In fact, they are floating on rafts of reeds.
Some are the most elaborate constructions,
yet all these soaring arches and roofs are also made from bundles of reeds.
And reeds provide food for the livestock, so gathering them is a daily and never-ending chore.
The herds have to be as much at home in the water are they are on their floating platforms
The rewards of this precarious existence are, of course,
the abundant fish which live all around the houses and even underneath them.
So the fish and the marsh Arabs and the pelicans all flourish in one integrated community.
The river has delivered the minerals it eroded from the mountains
and the nutrients it collected from the forests.
They sustain plants which are the food for small animals which are eaten by fish
and which are gathered by great flocks of birds
that, from the tropics to the Arctic, are the glories of the deltas.
A blizzard of snow geese in northern Canada.
Across the world in the tropics, on a delta in Papua New Guinea, magpie geese.
In Australia, brolga cranes.
Scarlet ibis in Venezuela.
Plovers on almost any delta in the world. And, equally widespread, stilts.
Flamingos in Africa.
And spoonbills.
Of all the deltas in the world, none is greater than that of the Amazon.
For hundreds of miles along its lower course,
the river has been so broad that it has been impossible to see from one side to another.
Now, instead of receiving more tributaries, it splits into a tangle of separate channels.
And on the last firm land on its banks stands a great and thriving port,
for the river is so wide and deep that cargo ships from overseas
can use it as a highway that can take them for 1,000 miles into the heart of South America.
The Amazon's vital statistics are astounding.
At any one time, two thirds of all the river water in the world is flowing between its banks.
Here at its mouth, at Belem, it's 200 miles across a maze of channels and islands,
one of which is, alone, bigger than the whole of Switzerland.
The river maintains its identity far into the sea. It was because of this that it was discovered.
In 1499 a Spanish sea captain, sailing well beyond the sight of land,
suddenly became aware that the water he was crossing was fresh and not salty.
He turned west and discovered this immense river.
Indeed, it's not until 100 miles beyond the edge of the continent
that particles of water which fell on the Andes complete their 4,000-mile-long journey
and mingle with the salt water of the ocean.
But along the coast, where the thrust of the river flood is not so great, is a halfway house.
Here the water is neither fresh nor salt, but brackish.
It's neither land nor sea, but banks of mud and sand
that are half the time submerged and half the time exposed.
And that intermediate, ever-changing territory is where we will be next time.