0:01:09 > 0:01:11A strangely-shaped mountain
0:01:11 > 0:01:16catching the clouds high above the jungles of Venezuela.
0:01:16 > 0:01:22Its summit rocks are carved into a multitude of grotesque shapes.
0:01:22 > 0:01:26The sculptor is an agent continuously at work
0:01:26 > 0:01:29on the landscapes of our planet rainwater.
0:01:29 > 0:01:32It washes over the rock,
0:01:32 > 0:01:35eroding it chemically.
0:01:35 > 0:01:37It permeates the cracks,
0:01:37 > 0:01:42freezes and chips it off in flakes and splinters.
0:01:44 > 0:01:49As the water flows down, it starts on a long journey
0:01:49 > 0:01:51from the rainy mountains to the sea
0:01:51 > 0:01:55and here, with a leap of over 3,000 ft,
0:01:55 > 0:01:59it forms the Angel Falls.
0:02:12 > 0:02:16Our journey begins not far from that towering waterfall,
0:02:16 > 0:02:22on the high moorlands of Peru, 15,000 ft above the sea.
0:02:34 > 0:02:39Water is a very extraordinary and very precious substance.
0:02:39 > 0:02:42It's the only substance, apart from mercury,
0:02:42 > 0:02:45which stays liquid at normal temperatures.
0:02:45 > 0:02:50Because of that, it's an essential part of all living organisms,
0:02:50 > 0:02:52animals and plants.
0:02:52 > 0:02:55Without it, life would come to an end.
0:02:55 > 0:02:59This particular water is a very rare kind.
0:02:59 > 0:03:0397% of the water on earth is salty the sea.
0:03:03 > 0:03:07But THIS was distilled from the surface of the sea by the sun,
0:03:07 > 0:03:11rose into the sky and condensed to form clouds,
0:03:11 > 0:03:14and fell again as rain and snow
0:03:14 > 0:03:19to form streams of pure, fresh, sweet water.
0:03:19 > 0:03:24This particular stream is on its way to the sea
0:03:24 > 0:03:26a very long way away.
0:03:26 > 0:03:28Because these are the Andes,
0:03:28 > 0:03:35and this is one of the many streams feeding the biggest river on earth,
0:03:35 > 0:03:37the Amazon.
0:03:39 > 0:03:44The difficulties of living in this young, violent river are formidable.
0:03:44 > 0:03:47Its waters are thick with rock and mud
0:03:47 > 0:03:49but they contain few nutrients.
0:03:49 > 0:03:53They rush down the valley at tremendous speed.
0:03:53 > 0:03:57Anything living here has to be a prodigious swimmer.
0:03:57 > 0:04:00And these are. They're torrent ducks.
0:04:14 > 0:04:18They exploit the swirls and eddies with consummate skill,
0:04:18 > 0:04:21paddling with their large webbed feet.
0:04:21 > 0:04:23They head always upstream,
0:04:23 > 0:04:27bracing themselves against rocks with their stiff-quilled tails
0:04:27 > 0:04:31and using small horny spurs on the wrists of their wings
0:04:31 > 0:04:34to give them purchase.
0:04:36 > 0:04:39A pair owns a stretch of the river,
0:04:39 > 0:04:43working up it until they reach the edge of their territory.
0:04:43 > 0:04:48Then they are swept downstream to begin all over again.
0:05:03 > 0:05:06Anchored firmly to the rocks
0:05:06 > 0:05:09is a kind of moss.
0:05:09 > 0:05:12Mosses are primitive ancient plants
0:05:12 > 0:05:16that grew on earth long before flowering plants.
0:05:16 > 0:05:21Torrent moss grows in young rivers and streams all over the world.
0:05:21 > 0:05:25Wherever it grows, in the Andes or here in Europe,
0:05:25 > 0:05:29it provides shelter for a multitude of insect larvae.
0:05:30 > 0:05:32In summer, they are transformed,
0:05:32 > 0:05:35briefly leaving the river to mate.
0:05:35 > 0:05:38But most of their lives are spent underwater.
0:05:38 > 0:05:42Some are streamlined against the current.
0:05:42 > 0:05:47- Caddis fly- larvae live in protective tubes:
0:05:47 > 0:05:52hollow stems, or a construction of wood stuck together with silk.
0:05:55 > 0:05:59Some weight themselves down so the current doesn't shift them
0:05:59 > 0:06:03by building their shelters from heavy grains of sand.
0:06:07 > 0:06:09The larva of the blackfly
0:06:09 > 0:06:12holds on to a pebble with its back end
0:06:12 > 0:06:17and grabs at passing food particles with the antennae on its head.
0:06:17 > 0:06:22It grips the rock with a ring of hooks, but if it loses its hold,
0:06:22 > 0:06:24all is not lost.
0:06:25 > 0:06:28It has a lifeline of silk
0:06:28 > 0:06:31which it has attached to its pebble.
0:06:45 > 0:06:48Having hauled itself back,
0:06:48 > 0:06:50it has to get a new grip.
0:06:50 > 0:06:54It spins a pad of silk from a hole beneath its mouth
0:06:54 > 0:06:57and fixes its hooks into that.
0:06:58 > 0:07:03The nets it collects food with are modified antennae
0:07:03 > 0:07:05and the larva brushes off its catch
0:07:05 > 0:07:09with alternate flicks of its mouth parts.
0:07:12 > 0:07:15Not all caddis larvae live in solid tubes.
0:07:15 > 0:07:18This one lives in a construction
0:07:18 > 0:07:22that is also a food-catching device.
0:07:27 > 0:07:29It uses its silk
0:07:29 > 0:07:32to produce a funnel-shaped scaffold of crossed threads.
0:07:41 > 0:07:44Undulating its body helps its breathing,
0:07:44 > 0:07:48speeding the flow of oxygen-bearing water
0:07:48 > 0:07:50through the funnel.
0:07:52 > 0:07:56It holds on with the hooks at the back...
0:07:58 > 0:08:04..leaving its jaws and front legs free to do the construction work.
0:08:29 > 0:08:31This blackfly larva
0:08:31 > 0:08:34wasn't saved by its lifeline.
0:08:57 > 0:08:59But the caddis-fly larva itself,
0:08:59 > 0:09:04ferocious and artful trapper though it is,
0:09:04 > 0:09:06is also at risk.
0:09:08 > 0:09:10The dipper relishes it.
0:09:13 > 0:09:17Dippers live in the rivers of North America and Europe.
0:09:19 > 0:09:24Under water, their swimming is different from the torrent ducks'.
0:09:24 > 0:09:27Its feet aren't webbed like a duck's
0:09:27 > 0:09:31so it uses its wings to "fly" under water.
0:09:48 > 0:09:52In similar cold, fast-flowing streams in North America
0:09:52 > 0:09:56lives a giant newt, the hell-bender.
0:09:56 > 0:10:00When it is young, it takes insect larvae.
0:10:00 > 0:10:02But it can grow to over two feet long
0:10:02 > 0:10:05and then it seeks much bigger prey.
0:10:07 > 0:10:10A crayfish would suit it admirably.
0:10:13 > 0:10:16A narrow escape.
0:10:16 > 0:10:19The crayfish saved itself by a snap of its tail.
0:10:19 > 0:10:22But the hell-bender doesn't give up easily.
0:10:27 > 0:10:30Both animals try to keep out of the current
0:10:30 > 0:10:33and habitually creep into crevices.
0:10:44 > 0:10:48But that, sometimes, is a mistake.
0:11:09 > 0:11:15Small streams tumbling down the sides of valleys to young rivers
0:11:15 > 0:11:17have their own population.
0:11:19 > 0:11:23The big-headed turtle clambers around the waterfalls
0:11:23 > 0:11:26using its tail as a prop.
0:11:35 > 0:11:39In West African waterfalls, and nowhere else,
0:11:39 > 0:11:41lives the extraordinary hairy frog.
0:11:44 > 0:11:48Its hairs are filaments of skin on its flanks
0:11:48 > 0:11:53which act as gills, helping it absorb oxygen from the water.
0:11:54 > 0:11:57And, almost as unusual,
0:11:57 > 0:12:01it has claws that help it grip the slippery stones.
0:12:17 > 0:12:19The many sources of the Amazon
0:12:19 > 0:12:23began as numberless rivulets in the eastern Andes.
0:12:23 > 0:12:25Now, 5,000 feet lower down,
0:12:25 > 0:12:30each has grown beyond recognition and cut its own zig-zag valley.
0:12:30 > 0:12:33White water tumbling down the valley wall
0:12:33 > 0:12:36joins the brown water of a larger tributary,
0:12:36 > 0:12:39heavy with mud and sediment.
0:12:42 > 0:12:45And as it gets bigger and bigger,
0:12:45 > 0:12:49it becomes more and more powerful.
0:12:49 > 0:12:53It's the dry season now, and the river is comparatively low.
0:12:53 > 0:12:57But during the rains when it's in spate, its waters rise
0:12:57 > 0:12:59above here.
0:12:59 > 0:13:02And the sheer volume and weight and force of them
0:13:02 > 0:13:06can shift boulders the size of these.
0:13:19 > 0:13:23The volume and speed of its waters
0:13:23 > 0:13:26are not the river's only weapons.
0:13:28 > 0:13:30It also has teeth,
0:13:30 > 0:13:35and in this empty part of its bed, you can see them.
0:13:39 > 0:13:41Sand and gravel.
0:13:41 > 0:13:46Fragments of rock that were eroded from higher up in its course
0:13:46 > 0:13:49which the river hurls with enormous force
0:13:49 > 0:13:52at the rocks of its river bed.
0:13:55 > 0:14:00With such tools, it can carve away the sides of mountains.
0:14:14 > 0:14:17Young, vigorous rivers transform the land,
0:14:17 > 0:14:19demolishing the mountains,
0:14:19 > 0:14:23breaking down the debris into smaller particles
0:14:23 > 0:14:26and carrying them downstream.
0:14:26 > 0:14:29This river in China is always so turbid
0:14:29 > 0:14:32that it's called the Huang Ho, the Yellow River.
0:14:32 > 0:14:35It carries more sediment than any other river.
0:14:35 > 0:14:39During floods, each cubic yard of water
0:14:39 > 0:14:44contains over 2,000 pounds of soil and pulverised rock.
0:14:54 > 0:15:00Rivers in the full vigour of their youth are terrifyingly strong.
0:15:00 > 0:15:03They roll great boulders along their beds,
0:15:03 > 0:15:05they cut away at the banks,
0:15:05 > 0:15:10undermining trees which crash into the water and are swept away.
0:15:17 > 0:15:21When a river encounters a band of unusually hard rock,
0:15:21 > 0:15:24like an ancient flow of basalt lava,
0:15:24 > 0:15:27its progress is temporarily slowed.
0:15:27 > 0:15:31It spreads out over the barrier and tumbles over the edge.
0:15:31 > 0:15:35So some of the loveliest cascades are formed.
0:15:35 > 0:15:40These are the Falls of Iguazu on the Brazil-Paraguay border.
0:15:40 > 0:15:43They can't compare in height with the Angel Falls,
0:15:43 > 0:15:47but in terms of the volume of water passing over them,
0:15:47 > 0:15:50they are incomparably bigger.
0:15:59 > 0:16:04The falling waters pound away at the base of the Falls,
0:16:04 > 0:16:08undercutting the basalt until blocks split off the face.
0:16:08 > 0:16:11So the falls steadily work their way upriver,
0:16:11 > 0:16:14leaving a deep gorge downstream.
0:16:14 > 0:16:19And animals live even here, within the Falls themselves.
0:16:20 > 0:16:25Swifts perch on the rock face, behind the cascade.
0:16:25 > 0:16:29Every evening they congregate high above Iguazu.
0:16:29 > 0:16:33After a day of hunting insects, they are ready to roost.
0:16:33 > 0:16:37And where safer than behind a screen of falling water?
0:16:40 > 0:16:43Some dive down with such speed
0:16:43 > 0:16:47that they shoot right through the fall.
0:16:58 > 0:17:02Now the river has left the mountains far behind,
0:17:02 > 0:17:05and has changed its character considerably.
0:17:05 > 0:17:07It's bigger, it's broader,
0:17:07 > 0:17:10and its waters carry not only sand and gravel
0:17:10 > 0:17:15but rich nutrients washed in from its vegetation-covered banks.
0:17:15 > 0:17:20After it goes over its last rapids and tumbles over its last fall,
0:17:20 > 0:17:24it becomes a very different river indeed.
0:17:29 > 0:17:35It's middle-aged. Ampler, less violent, more sluggish,
0:17:35 > 0:17:37and richer.
0:17:39 > 0:17:41Beside the Amazon tributaries,
0:17:41 > 0:17:44the jungle stands thick.
0:17:44 > 0:17:49Birds like the sun-bittern stalk quietly in search of a meal.
0:17:50 > 0:17:54Huge fish cruise through the slow waters.
0:17:56 > 0:18:01The arapaima, one of the largest of freshwater fish,
0:18:01 > 0:18:03grows over six feet long.
0:18:03 > 0:18:07The Amazon contains over 3,000 different kinds of fish.
0:18:07 > 0:18:11That's more than live in all the Atlantic.
0:18:14 > 0:18:17Rays probably evolved in the sea,
0:18:17 > 0:18:20but this species has made the change to fresh water
0:18:20 > 0:18:23and lives high up the Amazon.
0:18:23 > 0:18:26Many other fish have evolved here in fresh water,
0:18:26 > 0:18:32adapting to all its variations of depth, speed and chemical content,
0:18:32 > 0:18:34to muddy water and to clear,
0:18:34 > 0:18:37to areas thick with plants
0:18:37 > 0:18:39and places where there are none.
0:18:39 > 0:18:41Their variety is enormous.
0:18:43 > 0:18:47Take, for example, just one family, the catfish.
0:18:47 > 0:18:51They are bottom-dwelling fish, with feelers on their snouts
0:18:51 > 0:18:53that have sense organs on them,
0:18:53 > 0:18:56so the fish can feel and taste their way
0:18:56 > 0:19:00through the thick muddy water, or at night.
0:19:00 > 0:19:02There are small ones and huge ones,
0:19:02 > 0:19:06some that give electric shocks, others that swim upside down.
0:19:06 > 0:19:09Those living in fast-flowing waters
0:19:09 > 0:19:12have suckers on their chins or bellies
0:19:12 > 0:19:15with which they cling to rocks.
0:19:15 > 0:19:19In South America alone,
0:19:19 > 0:19:22there are 1,200 different species of catfish.
0:19:48 > 0:19:51In these crowded waters
0:19:51 > 0:19:54many fish give special protection to their young
0:19:54 > 0:19:56for the first weeks of their lives.
0:19:56 > 0:19:59The discus fish goes even further.
0:19:59 > 0:20:03It provides its fry with special food.
0:20:03 > 0:20:07Parents exude a nutritious slime from their skin
0:20:07 > 0:20:11and the young graze over their flanks, feeding on it.
0:20:44 > 0:20:49In a week they're big enough to feed on small floating particles.
0:21:01 > 0:21:03These are now a month old,
0:21:03 > 0:21:08and have already assumed the disc-like shape of their parents.
0:21:08 > 0:21:10They're becoming independent,
0:21:10 > 0:21:14but they're too near the lair of an electric eel.
0:21:16 > 0:21:18The eel has very poor eyesight
0:21:18 > 0:21:21but it detects the presence of objects around it
0:21:21 > 0:21:25with short electric discharges, like radar.
0:21:25 > 0:21:27It rises for a gulp of air.
0:21:27 > 0:21:32This time the young discus seem to have escaped detection.
0:21:39 > 0:21:44But the eel can produce a major electric shock to stun its prey.
0:21:58 > 0:22:01Astonishingly it releases its captive.
0:22:01 > 0:22:04Perhaps it's too small to eat.
0:22:04 > 0:22:09The young discus, apart from the eel's jaw marks on its flanks,
0:22:09 > 0:22:11seems no worse off.
0:22:11 > 0:22:13One Amazonian fish puts its eggs
0:22:13 > 0:22:17beyond the reach of any water-living predator,
0:22:17 > 0:22:20on leaves overhanging a river.
0:22:20 > 0:22:23A pair of splashing tetras are courting.
0:22:25 > 0:22:28Curving their bodies, for a moment
0:22:28 > 0:22:30they leap clear of the water.
0:22:31 > 0:22:34Sometimes a third fish joins in.
0:22:39 > 0:22:42The bigger of the two is the male.
0:22:42 > 0:22:45For a moment they hang on the leaf
0:22:45 > 0:22:49supported by the suction of the male's floppy fins.
0:22:51 > 0:22:54Again and again they jump.
0:22:54 > 0:22:58In this moment the female lays her eggs and drops off
0:22:58 > 0:23:03and the male fertilises them. Each time they leave 12 or so eggs.
0:23:10 > 0:23:14A few infertile eggs drop off the leaf and are eaten.
0:23:14 > 0:23:19Eventually, 200 eggs are placed out of harm's way.
0:23:19 > 0:23:23And the river can be an exceedingly dangerous place.
0:23:23 > 0:23:27Piranha, the most savage of all the Amazon fish.
0:23:27 > 0:23:31A swimming capybara realises their presence and tries to retreat
0:23:31 > 0:23:33too late.
0:23:38 > 0:23:41The splashing, the taste of blood
0:23:41 > 0:23:44spreading through the water
0:23:44 > 0:23:48attracts more of the shoal until there are hundreds of fish
0:23:48 > 0:23:50possessed by a frenzy for flesh.
0:23:50 > 0:23:54They're only a foot long, but their teeth cut clean through bone.
0:24:03 > 0:24:06In minutes, there is little left.
0:24:09 > 0:24:13As the river gets older, it slows down.
0:24:13 > 0:24:16A minor obstacle in its path will deflect it.
0:24:16 > 0:24:20Water flowing round the outside of a bend has to travel farther
0:24:20 > 0:24:22and speeds up, eroding the bank.
0:24:22 > 0:24:25Inside the bend the current is slow
0:24:25 > 0:24:29and the water drops its heavy sediment to form a shoal.
0:24:29 > 0:24:32So the bend gets more exaggerated
0:24:32 > 0:24:35as the elderly river swings from side to side
0:24:35 > 0:24:38with many loops and meanders.
0:24:38 > 0:24:40One bend approaches another
0:24:40 > 0:24:44until the land between them is so narrow it collapses.
0:24:44 > 0:24:46The river takes the shorter course,
0:24:46 > 0:24:51and the meander is left isolated as a curving lake.
0:24:51 > 0:24:54There the water, at last, is still.
0:24:54 > 0:24:57Plants no longer have to fight a current
0:24:57 > 0:25:00and the lakes become clogged with vegetation.
0:25:00 > 0:25:04These are the largest floating leaves of all,
0:25:04 > 0:25:08the leaves of the famous giant Amazon lily.
0:25:08 > 0:25:12Covering the water with huge leaves is a very aggressive act,
0:25:12 > 0:25:15for it cuts out the light in the water below
0:25:15 > 0:25:18making it hard for other plants to grow.
0:25:18 > 0:25:21The upturned rims of the pads as they grow
0:25:21 > 0:25:25thrust aside all other floating plants.
0:25:25 > 0:25:30And to prevent these leaves from being eaten by fish,
0:25:30 > 0:25:35they're protected by very effective ferocious spines underneath,
0:25:35 > 0:25:38as you can see most clearly on this half-opened bud.
0:25:38 > 0:25:40It grows from the size of a plate
0:25:40 > 0:25:45to a huge disc six feet across in a few days,
0:25:45 > 0:25:48growing by one square inch every minute.
0:25:48 > 0:25:51The flowers develop as quickly.
0:25:51 > 0:25:53They open first in the evening
0:25:53 > 0:25:57and remain with petals spread, powerfully fragrant, all night.
0:25:57 > 0:26:00By morning it's closed again.
0:26:00 > 0:26:04But during the night it's taken prisoners.
0:26:04 > 0:26:06Inside the flower
0:26:06 > 0:26:08are beetles.
0:26:08 > 0:26:12Sometimes up to 40 in a single bloom.
0:26:12 > 0:26:17They're attracted by special sugary outgrowths
0:26:17 > 0:26:19in the centre of the flower,
0:26:19 > 0:26:22and while they are trapped
0:26:22 > 0:26:24they will feed on those.
0:26:24 > 0:26:26This evening the flower opens again
0:26:26 > 0:26:31to release the beetles, which will fly off carrying pollen
0:26:31 > 0:26:34to cross-pollinate another lily flower.
0:26:34 > 0:26:36Then, after just two nights,
0:26:36 > 0:26:39this bloom, by now turned purple,
0:26:39 > 0:26:41will crumple and die.
0:26:45 > 0:26:50The immense leaves, strengthened by air-filled ribs beneath,
0:26:50 > 0:26:52can support a small child.
0:26:52 > 0:26:56And water birds can walk over them with total confidence and safety.
0:27:00 > 0:27:04The jacana has elongated toes that spread its weight so well
0:27:04 > 0:27:09that it can tread on much flimsier leaves than those of this lily,
0:27:09 > 0:27:11without submerging them.
0:27:11 > 0:27:14It seeks insects, and there are plenty of them.
0:27:14 > 0:27:19The pond skater sits on a leaf, but it can also sit on the water.
0:27:19 > 0:27:24The surface is a springy platform that supports many small creatures.
0:27:24 > 0:27:29Water molecules are bound to one another by a force like magnetism.
0:27:29 > 0:27:32They're not attracted to molecules of air, above,
0:27:32 > 0:27:36so surface molecules have their forces concentrated sideways,
0:27:36 > 0:27:39giving the surface a very strong tension.
0:27:39 > 0:27:42And the pond skater hunts on it.
0:27:42 > 0:27:45It's lost its prey under the leaf.
0:27:48 > 0:27:50This time there is no escape.
0:27:50 > 0:27:54The pond skater stabs its victim and sucks it dry.
0:27:54 > 0:27:59It's important for the pond skater to keep meticulously clean.
0:27:59 > 0:28:02Its waxy body and hairy feet repel water,
0:28:02 > 0:28:05but any dirt on them that is wettable
0:28:05 > 0:28:08breaks the surface tension film.
0:28:09 > 0:28:11They're aggressive insects,
0:28:11 > 0:28:15each with its own territory among the lily pads.
0:28:17 > 0:28:21Intruders are immediately chased away,
0:28:21 > 0:28:24and fights between rivals are common.
0:28:26 > 0:28:30The surface tension film is the pond skaters' platform
0:28:30 > 0:28:32and their sounding board.
0:28:32 > 0:28:36Sense organs on their feet detect the vibrations
0:28:36 > 0:28:41caused by a struggling insect that has fallen on the surface.
0:28:41 > 0:28:45By bouncing up and down, they communicate to one another,
0:28:45 > 0:28:47warning off rivals
0:28:47 > 0:28:51and sending come-hither signals to potential mates.
0:29:02 > 0:29:05Whirligig beetles use surface vibrations
0:29:05 > 0:29:07in a different way.
0:29:07 > 0:29:11By gyrating, they create ripples,
0:29:11 > 0:29:15and the returning echoes show the presence of other creatures
0:29:15 > 0:29:17and obstacles around them.
0:29:20 > 0:29:23They have excellent eyes which are partitioned
0:29:23 > 0:29:25so that the lower half peers down
0:29:25 > 0:29:28to see what's happening in the water beneath.
0:29:28 > 0:29:31Hanging below the surface is another hunter.
0:29:31 > 0:29:34Its tail has two tubes
0:29:34 > 0:29:38which penetrate the surface film to collect air for it to breathe.
0:29:38 > 0:29:43Its head has ferocious jaws to seize its prey.
0:29:43 > 0:29:46This is the larva of the giant diving beetle
0:29:46 > 0:29:49and it has caught a tadpole.
0:29:49 > 0:29:54It must come to the surface, even as an adult, to collect air
0:29:54 > 0:29:58to sustain it on its hunting forays into deeper waters.
0:30:00 > 0:30:04The water boatman patrols the surface looking for prey,
0:30:04 > 0:30:08not from above, like the pond skater, but from below.
0:30:08 > 0:30:11The two kinds of insects, between them,
0:30:11 > 0:30:15collect most of the creatures trapped in the surface film.
0:30:15 > 0:30:18The camphor beetle lives on plants by the water.
0:30:18 > 0:30:21It is the most versatile of all water walkers.
0:30:21 > 0:30:25It can run over water like a pond skater.
0:30:27 > 0:30:30It can produce a substance like camphor
0:30:30 > 0:30:33which reduces the tension between water molecules.
0:30:33 > 0:30:37In emergencies, it squirts this from its tail,
0:30:37 > 0:30:39and with tension reduced behind,
0:30:39 > 0:30:41but pulling hard at the front,
0:30:41 > 0:30:44it shoots across the surface so fast
0:30:44 > 0:30:46that you can only see it in slow motion.
0:30:48 > 0:30:51And, like other beetles,
0:30:51 > 0:30:53it can fly.
0:30:57 > 0:30:59One particularly ferocious hunter
0:30:59 > 0:31:03lives on the edge of lakes and ponds in Europe
0:31:03 > 0:31:06the fishing spider.
0:31:06 > 0:31:11It uses the surface tension film as other spiders use their webs.
0:31:11 > 0:31:14With its front legs resting on the surface,
0:31:14 > 0:31:16it feels for vibrations.
0:31:20 > 0:31:25But it also has excellent sight and can see prey below the surface.
0:31:28 > 0:31:32The stickleback sees only the spider's feet.
0:31:41 > 0:31:45That is a greatly slowed-down version of the kill.
0:31:45 > 0:31:47In reality, the pounce is rapier-swift
0:31:47 > 0:31:52and the stickleback had little chance once it came within range.
0:32:14 > 0:32:16The lakes and ponds fed by streams
0:32:16 > 0:32:19or cut off from the main course of the river
0:32:19 > 0:32:21are comparatively small.
0:32:21 > 0:32:25Where rivers flow into basins created by geological faults,
0:32:25 > 0:32:29their water accumulates in immense lakes.
0:32:29 > 0:32:32Lake Prespa in Yugoslavia is not the largest of lakes,
0:32:32 > 0:32:35but even so, it's 20 miles long.
0:32:35 > 0:32:40Rivers entering its still waters slow down and drop their sediment.
0:32:40 > 0:32:43So such lakes are potentially very fertile.
0:32:43 > 0:32:47Their animal inhabitants, no longer harassed by the current
0:32:47 > 0:32:53or hemmed in by a shallow bottom or narrow banks, can proliferate.
0:32:53 > 0:32:55Fish swarm in their waters.
0:33:02 > 0:33:06And fish-eating birds, like pelicans and cormorants,
0:33:06 > 0:33:08swarm correspondingly.
0:33:24 > 0:33:27Land based creatures haunt its margins.
0:33:27 > 0:33:29These are its most fertile parts,
0:33:29 > 0:33:34for the lack of strong currents in a deep lake
0:33:34 > 0:33:36starves the lower waters of oxygen.
0:33:36 > 0:33:39But in the shallows, warmed by the summer sun,
0:33:39 > 0:33:44algae and other plants flourish, small invertebrates proliferate
0:33:44 > 0:33:47and there is food for even the least agile hunters.
0:34:11 > 0:34:14In one way, these large lakes are very special.
0:34:14 > 0:34:19This trout with distinctive red spots lives in Lake Ohrid,
0:34:19 > 0:34:24a few miles away from Lake Prespa, but nowhere else in the world.
0:34:24 > 0:34:27Isolated in a lake, fish become very inbred.
0:34:27 > 0:34:32Small characteristics that get lost in bigger populations become fixed,
0:34:32 > 0:34:36and the fish evolve into new species.
0:34:36 > 0:34:39A similar thing has happened to the shrimps.
0:34:46 > 0:34:50And among the many species of water snails,
0:34:50 > 0:34:53several are now unique to Lake Ohrid.
0:34:57 > 0:35:03In central Russia lies a stretch of fresh water so huge and ancient
0:35:03 > 0:35:06that these processes have produced new species
0:35:06 > 0:35:10on a scale unequalled anywhere else in the world.
0:35:10 > 0:35:12Lake Baikal.
0:35:13 > 0:35:16The lake lies in a great depression
0:35:16 > 0:35:19formed by faulting in the earth's crust.
0:35:19 > 0:35:21It's 400 miles long
0:35:21 > 0:35:26and 5,000 feet deep, the deepest of all lakes.
0:35:28 > 0:35:31In the depths of the lake, 1,000 feet down,
0:35:31 > 0:35:35lives a unique salmon, the omul.
0:35:35 > 0:35:37In summer they move to the shallows
0:35:37 > 0:35:41and feed on caddis fly larvae and sand hoppers
0:35:41 > 0:35:45and here they are caught in great numbers, for they're delicious.
0:35:54 > 0:35:59This is only one of Baikal's special inhabitants.
0:35:59 > 0:36:03Of the 1,200 different kinds of fish and other animals
0:36:03 > 0:36:06and the 500 plants it contains,
0:36:06 > 0:36:08over 80% are unique.
0:36:08 > 0:36:11There are unique molluscs, unique flatworms,
0:36:11 > 0:36:15and even one unique mammal, the Baikal seal.
0:36:18 > 0:36:25This tiny seal is descended from the ringed seal of the Arctic sea.
0:36:25 > 0:36:29Today the lake is over 1,000 miles away from that sea.
0:36:29 > 0:36:32The ancestors of these seals arrived in the Ice Age,
0:36:32 > 0:36:36when the journey was shorter and easier.
0:36:38 > 0:36:42Cut off from other seals, they've developed in their own way.
0:36:42 > 0:36:46The Amazon has no great lake on its course,
0:36:46 > 0:36:50so even in its middle stretches
0:36:50 > 0:36:52it carries mud from the Andes.
0:36:52 > 0:36:57The Rio Negro, joining it here, is clear it comes from the northwest
0:36:57 > 0:36:59where the rocks are hard and bare.
0:36:59 > 0:37:03The two huge rivers flow alongside one another in the same bed,
0:37:03 > 0:37:06scarcely mixing.
0:37:06 > 0:37:10As well as sediment, they carry abundant nutrients
0:37:10 > 0:37:14and life on their banks flourishes as never before.
0:37:14 > 0:37:17Herds of capybara wade through the shallows
0:37:17 > 0:37:20cropping the luxuriant plants.
0:37:25 > 0:37:29They are excellent swimmers, with webs between their toes,
0:37:29 > 0:37:33and they have that placing of eyes, ears and nose
0:37:33 > 0:37:38so valuable to mammals that regularly swim on top of the head
0:37:38 > 0:37:42so that the submerged animal can see, hear and smell
0:37:42 > 0:37:44what is going on above water around them.
0:37:57 > 0:38:00Giant otters have a similar head design,
0:38:00 > 0:38:03and sometimes lift themselves above the surface
0:38:03 > 0:38:05to get an even better view.
0:38:10 > 0:38:14This Amazonian species is the biggest of all the world's otters,
0:38:14 > 0:38:17six feet long and a powerful swimmer,
0:38:17 > 0:38:20equipped with large webbed feet,
0:38:20 > 0:38:25a flattened tail and sensitive whiskers.
0:38:25 > 0:38:28A pair makes territorial patches on the river bank,
0:38:28 > 0:38:31marking them with their own personal smell.
0:38:41 > 0:38:45There are otters in many of the great rivers of the world,
0:38:45 > 0:38:48and they are the most graceful of swimmers.
0:39:02 > 0:39:07In India they share the fish harvest with the gavial.
0:39:07 > 0:39:11Most adult members of the crocodile family feed largely on carrion
0:39:11 > 0:39:14but the gavial eats only fish.
0:39:14 > 0:39:16It has long, narrow jaws
0:39:16 > 0:39:21studded with abundant teeth, for catching them underwater.
0:39:22 > 0:39:25Birds also claim a share of the river fish.
0:39:27 > 0:39:29The hooded merganser,
0:39:29 > 0:39:33one of a group of ducks called sawbills.
0:39:39 > 0:39:44Its beak, like the gavial's jaws, is long and narrow
0:39:44 > 0:39:47so it is easily snapped together under water.
0:39:47 > 0:39:49It has a notched edge
0:39:49 > 0:39:51to grip slippery fish.
0:39:52 > 0:39:57But their feathers trap so much air that the pair must work very hard
0:39:57 > 0:40:00to get down to any depth.
0:40:00 > 0:40:03Coming up again is easy enough.
0:40:03 > 0:40:05But the meal is a mere mouthful
0:40:05 > 0:40:09and the merganser must must look for another one.
0:40:11 > 0:40:15On the bottom lurks more danger for a fish.
0:40:15 > 0:40:17A worm, perhaps?
0:40:21 > 0:40:25No, the deceiving tongue of a turtle.
0:40:54 > 0:40:58And in the sky above the river, more trouble for a fish.
0:41:07 > 0:41:10The kingfisher.
0:41:34 > 0:41:37There's one left for next time.
0:41:39 > 0:41:42The fish eagle is not a diver,
0:41:42 > 0:41:46but a pouncer with marvellously co-ordinated action.
0:41:49 > 0:41:53The aerial onslaught on fish goes on all day
0:41:53 > 0:41:55and night.
0:41:55 > 0:41:58An owl goes fishing in Africa.
0:42:01 > 0:42:03Its legs are bare.
0:42:03 > 0:42:06Feathers would drag in the water.
0:42:08 > 0:42:11Spines under its toes give it a firm grasp on fish.
0:42:44 > 0:42:46In the last phase of their life,
0:42:46 > 0:42:50great rivers often flow out of control.
0:42:50 > 0:42:55Their mountain tributaries, fed by the storms of the rainy season,
0:42:55 > 0:42:57pour so much water into them
0:42:57 > 0:43:00that they burst their banks.
0:43:00 > 0:43:02The Amazon rises every year,
0:43:02 > 0:43:06to flood tens of thousands of miles of forest,
0:43:06 > 0:43:09in some parts as much as 40 feet deep.
0:43:14 > 0:43:19Some of these trees are flooded for eight to 10 months every year.
0:43:19 > 0:43:22They need only two months annually out of water
0:43:22 > 0:43:26for them to grow and for their seeds to germinate and sprout.
0:43:26 > 0:43:28We still don't know how they manage it.
0:43:36 > 0:43:40As the floods well out over the land,
0:43:40 > 0:43:43fish from the river travel with them.
0:43:43 > 0:43:47This is going to be their best feeding time of the year.
0:43:51 > 0:43:54As it is for other creatures too.
0:43:59 > 0:44:04Among the fallen leaves on the bottom lies the mata-mata turtle,
0:44:04 > 0:44:09marvellously camouflaged, waiting for a decent-sized fish.
0:44:23 > 0:44:25And there are plenty already here,
0:44:25 > 0:44:30sheltering, like the turtle, among the still-unrotted leaves.
0:44:36 > 0:44:40Piranha are here, too not the flesh-eating kind,
0:44:40 > 0:44:43Their teeth are used for something different.
0:44:43 > 0:44:45Fruit.
0:45:02 > 0:45:06As the river becomes older and older,
0:45:06 > 0:45:09its riches increase still further.
0:45:11 > 0:45:14All over the world, as rivers approach their end,
0:45:14 > 0:45:17they deposit the sand and mud
0:45:17 > 0:45:21that they have gathered from so far and carried for so long.
0:45:21 > 0:45:24In many parts of the world,
0:45:24 > 0:45:26reeds grow thickly on these banks.
0:45:26 > 0:45:31Their stems collect more sediment as the waters swirl through them.
0:45:31 > 0:45:35Living in the dense reed beds requires great skill.
0:45:35 > 0:45:38The little bittern somehow finds its nest
0:45:38 > 0:45:43hidden out of sight in this seemingly uniform stretch of reeds.
0:45:46 > 0:45:48It regurgitates from its crop
0:45:48 > 0:45:52ample supplies of fish and frogs for its young.
0:46:03 > 0:46:07Their world is an infinity of vertical stems,
0:46:07 > 0:46:10but they are nimble climbers from an early age
0:46:10 > 0:46:14and they leave the nest within a few days of hatching.
0:46:21 > 0:46:24There they wait, almost invisible,
0:46:24 > 0:46:28for their parents to return with re-stocked crops.
0:46:46 > 0:46:51The reed-clogged waters of a river delta are full of potential riches,
0:46:51 > 0:46:54not only for birds but for humans.
0:46:54 > 0:46:59The reeds are used for many purposes, but it's not an easy life.
0:46:59 > 0:47:03Firm land on which to live is hard to find.
0:47:03 > 0:47:08In the Danube delta, the few solid sandbanks are packed with houses.
0:47:08 > 0:47:11Earth is carefully conserved with piles
0:47:11 > 0:47:15to stop a change in the current from washing it away.
0:47:15 > 0:47:18There is the threat of a rise in the water level
0:47:18 > 0:47:20caused by heavy rains upstream
0:47:20 > 0:47:25or a very high tide, backed by a storm sweeping up from the sea,
0:47:25 > 0:47:28which can cause devastating floods.
0:47:30 > 0:47:34In the joined deltas of the Tigris and Euphrates in Iraq,
0:47:34 > 0:47:39the Marsh Arabs have become specialists in an amphibian life.
0:47:45 > 0:47:49Their houses seem to have solid enough foundations.
0:47:49 > 0:47:53In fact, they are floating on rafts of reeds.
0:48:10 > 0:48:13Some are the most elaborate constructions,
0:48:13 > 0:48:19yet these soaring arches and roofs are made from bundles of reeds.
0:48:19 > 0:48:23And reeds provide food for the livestock.
0:48:23 > 0:48:27So gathering them is a daily and never-ending chore.
0:48:41 > 0:48:43The herds have to be
0:48:43 > 0:48:45as much at home in the water
0:48:45 > 0:48:48as they are on their floating platforms.
0:48:55 > 0:49:00The rewards of this precarious existence are the abundant fish
0:49:00 > 0:49:04which live all around the houses and even underneath them.
0:49:08 > 0:49:10So the fish, the Marsh Arabs,
0:49:10 > 0:49:14and the pelicans all flourish in one integrated community.
0:49:14 > 0:49:17The river has finally delivered
0:49:17 > 0:49:22the minerals from the mountains and the nutrients from the forests.
0:49:22 > 0:49:26They sustain plants, the food for small animals,
0:49:26 > 0:49:28which are eaten by bigger fish,
0:49:28 > 0:49:31which are ultimately gathered by the great flocks of birds
0:49:31 > 0:49:34that are the glories of the deltas.
0:49:40 > 0:49:44A blizzard of snow geese in northern Canada.
0:49:50 > 0:49:54Across the world in the tropics, in Papua New Guinea,
0:49:54 > 0:49:56magpie geese.
0:50:03 > 0:50:07In Australia, brolga cranes.
0:50:15 > 0:50:18Scarlet ibis in Venezuela.
0:50:20 > 0:50:22Plovers all over the world.
0:50:22 > 0:50:25And equally widespread, stilts.
0:50:41 > 0:50:44Flamingos in Africa.
0:50:53 > 0:50:55And spoonbills.
0:51:02 > 0:51:07Of all the deltas in the world, none is greater than the Amazon.
0:51:14 > 0:51:18For hundreds of miles along its lower course,
0:51:18 > 0:51:20the river has been so wide
0:51:20 > 0:51:24that you can't see from one side to the other.
0:51:24 > 0:51:27Now, instead of receiving water,
0:51:27 > 0:51:29it splits into a tangle of several channels.
0:51:31 > 0:51:37On the last firm land on its banks stands a great thriving port,
0:51:37 > 0:51:40for the river is so wide and deep
0:51:40 > 0:51:42that cargo ships from overseas
0:51:42 > 0:51:45can use it as a highway
0:51:45 > 0:51:50that takes them 1,000 miles into the heart of South America.
0:51:50 > 0:51:53The Amazon's vital statistics are astounding.
0:51:53 > 0:51:57At any one time, two thirds of all the river water in the world
0:51:57 > 0:52:00is flowing between its banks.
0:52:00 > 0:52:04Here at its mouth, at Belem, it's 200 miles across,
0:52:04 > 0:52:06a maze of channels and islands,
0:52:06 > 0:52:10one of which is bigger than the whole of Switzerland.
0:52:10 > 0:52:14The river maintains its identity far out into the sea.
0:52:14 > 0:52:16That's how it was discovered.
0:52:16 > 0:52:19In 1499, a Spanish sea-captain
0:52:19 > 0:52:22sailing well beyond the sight of land
0:52:22 > 0:52:27became aware that the water he was crossing was fresh and not salty,
0:52:27 > 0:52:31and he turned west and discovered this immense river.
0:52:31 > 0:52:35Indeed, it's not until 100 miles beyond the edge of the continent
0:52:35 > 0:52:39that particles of water that fell on the Andes
0:52:39 > 0:52:42complete their 4,000 mile long journey
0:52:42 > 0:52:45and mingle with the salt water of the ocean.
0:52:50 > 0:52:55Farther along the coast, the thrust of the river's flood is not so great,
0:52:55 > 0:52:57and there is a halfway house.
0:52:57 > 0:53:01The water is neither fresh nor salt, but brackish.
0:53:01 > 0:53:05It's neither land nor sea, but banks of mud and sand
0:53:05 > 0:53:08that are half the time submerged and half exposed.
0:53:08 > 0:53:12And that intermediate, ever-changing territory
0:53:12 > 0:53:14is where we will be next time.