1 00:00:54,988 --> 00:01:00,324 A strangely shaped mountain catching the clouds high above the jungles of Venezuela. 2 00:01:01,728 --> 00:01:06,062 Its summit rocks have been carved into a multitude of grotesque shapes. 3 00:01:06,366 --> 00:01:13,602 The sculptor, an agent that is continuously at wor on much of the landscape of our planet: Rainwater. 4 00:01:16,042 --> 00:01:19,239 It washes over the rock, eroding it chemically. 5 00:01:19,612 --> 00:01:25,573 It permeates the cracks, freezes, and chips it off in flakes and splinters. 6 00:01:29,189 --> 00:01:32,556 As the water flows downwards, it starts on a long journey 7 00:01:32,725 --> 00:01:35,751 that will take it from the mountains to the sea, 8 00:01:35,929 --> 00:01:40,957 and here, with a leap of over 3,000 feet, the highest made by any river, 9 00:01:41,201 --> 00:01:43,431 it forms the Angel Falls. 10 00:01:57,383 --> 00:02:01,046 Ourjourney begins not far from that towering waterfall 11 00:02:01,221 --> 00:02:07,057 on the high moorlands of Peru, 15,000 feet above the sea. 12 00:02:18,805 --> 00:02:23,640 Water is a very extraordinary and very precious substance, 13 00:02:23,810 --> 00:02:27,007 the only one on earth, apart from mercury, 14 00:02:27,280 --> 00:02:30,181 which remains liquid at normal temperatures and pressures, 15 00:02:30,416 --> 00:02:36,184 so it's an essential part of the bodies of all living organisms, animals and plant. 16 00:02:36,422 --> 00:02:39,357 Without it, life would come to an end. 17 00:02:39,993 --> 00:02:43,451 But this particular water is a very rare kind. 18 00:02:43,696 --> 00:02:47,359 97% of the water on earth is salty, the sea, 19 00:02:47,634 --> 00:02:52,003 but this was distilled from the surface of the sea by the heat of the sun, 20 00:02:52,205 --> 00:02:58,371 rose into the sky as vapour, condensed to form clouds and then fell again as rain and snow 21 00:02:58,545 --> 00:03:03,573 to form streams of pure, fresh, sweet water. 22 00:03:03,917 --> 00:03:10,186 But this particular stream is on its way to the sea a very long way away, 23 00:03:10,356 --> 00:03:14,952 because these are the Andes, and this is one of the many streams 24 00:03:15,128 --> 00:03:20,657 that can claim to be a source of the biggest river on earth, the Amazon. 25 00:03:23,937 --> 00:03:28,374 The difficulties of living in this young and violent river are formidable. 26 00:03:28,708 --> 00:03:33,805 Its waters are thick with powdered rock and mud, but they have gathered few nutrients, 27 00:03:34,147 --> 00:03:37,275 and they rush down the valley at tremendous speed. 28 00:03:37,650 --> 00:03:41,450 Anything that lives here has to be a prodigious swimmer. 29 00:03:42,088 --> 00:03:44,886 And these are. They're torrent ducks. 30 00:03:59,439 --> 00:04:02,772 They exploit the swirls and eddies with consummate skill, 31 00:04:02,942 --> 00:04:05,968 paddling with strokes of their large webbed feet. 32 00:04:06,212 --> 00:04:11,548 They head upstream, bracing themselves against rocks with their stiff quilled tail, 33 00:04:11,718 --> 00:04:16,519 and using small horny spurs on the wrists of their wings to give them purchase. 34 00:04:22,295 --> 00:04:27,665 A pair owns a stretch of the river, working their way up it to the frontier of their territory 35 00:04:27,834 --> 00:04:33,204 when they abandon themselves to the flood and are swept downstream to begin again. 36 00:04:48,688 --> 00:04:51,987 Anchored firmly to the rocks is a kind of moss. 37 00:04:54,193 --> 00:05:00,428 Mosses are primitive, ancient plants that appeared on earth long before flowering plants. 38 00:05:00,600 --> 00:05:04,969 This torrent moss is found in young rivers and streams all over the world, 39 00:05:05,238 --> 00:05:09,607 and wherever it grows, whether in the Andes or here in Europe, 40 00:05:09,809 --> 00:05:13,643 it provides shelter for a multitude of insect larv 41 00:05:15,481 --> 00:05:20,282 In summer, these creatures are transformed and fly briefly above the river to mate, 42 00:05:20,520 --> 00:05:23,353 but most of their lives are spent underwater. 43 00:05:23,723 --> 00:05:26,055 Some are streamlined against the current. 44 00:05:27,226 --> 00:05:31,458 The caddis fly larvae live in protective tubes, the hollow stem of a reed, 45 00:05:31,631 --> 00:05:35,192 or a construction of bits of wood stuck together with silk. 46 00:05:39,505 --> 00:05:46,001 Some weight themselves down by building their shelters from heavy grains of sand. 47 00:05:51,818 --> 00:05:55,652 The larva of the blackfly holds on to a pebble with its back end, 48 00:05:55,822 --> 00:06:00,418 while it grabs at food particles that are swept past it with the antennae on its head. 49 00:06:02,161 --> 00:06:08,657 It grips the rock with a ring of hooks, but even if it loses its hold, all is not lost. 50 00:06:11,337 --> 00:06:15,797 It has a lifeline of silk which it has attached to its chosen pebble. 51 00:06:30,723 --> 00:06:34,090 Having hauled itself back, it now has to get a new grip. 52 00:06:34,260 --> 00:06:38,697 It spins a tiny pad of silk from a spinneretjust beneath its mouth, 53 00:06:38,898 --> 00:06:41,230 then it fixes its hooks into that. 54 00:06:43,903 --> 00:06:48,101 The nets with which it collects its food are modified antennae, 55 00:06:48,307 --> 00:06:53,176 and the larva brushes off what they catch with alternate flicks of its mouthparts. 56 00:06:57,116 --> 00:06:59,607 Not all caddis larvae live in solid tubes. 57 00:06:59,852 --> 00:07:05,051 This one builds a construction that serves both as a home and a food-gathering device. 58 00:07:11,831 --> 00:07:16,928 It uses its silk to produce a funnel-shaped scaffold of criss-crossing threads. 59 00:07:27,547 --> 00:07:30,414 Undulating its body is a way of aiding its breathing, 60 00:07:30,650 --> 00:07:34,518 for the movement speeds the flow of oxygen-bearing water through the funnel. 61 00:07:37,390 --> 00:07:39,483 It holds on with the hooks at the back... 62 00:07:43,529 --> 00:07:47,795 ...leaving its jaws and front legs free to do the construction work. 63 00:08:14,727 --> 00:08:18,458 This blackfly larva wasn't saved by its lifeline. 64 00:08:43,589 --> 00:08:49,425 But the caddis fly larva itself, ferocious and art trapper though it is, is also at risk. 65 00:08:53,466 --> 00:08:55,093 The dipper relishes it. 66 00:08:58,571 --> 00:09:02,029 Dippers live both in the rivers of North America and Europe. 67 00:09:04,143 --> 00:09:08,910 Underwater, their swimming technique is quite different from the torrent ducks'. 68 00:09:09,582 --> 00:09:15,487 Its feet are not webbed like a duck's, so it propels itself with its wings, flying underwate 69 00:09:33,639 --> 00:09:36,836 In similar cold, fast-flowing streams in North America 70 00:09:37,009 --> 00:09:40,376 lives a kind of giant newt, the hellbender. 71 00:09:40,846 --> 00:09:44,373 When it's young, it also, like a dipper, takes insect larvae, 72 00:09:44,650 --> 00:09:50,088 but it can grow to over two feet long, and then it seeks much bigger prey. 73 00:09:52,258 --> 00:09:54,818 A crayfish would suit it admirably. 74 00:09:58,598 --> 00:10:04,332 A narrow escape. The crayfish saved itself at the last moment by a convulsive snap of its tail, 75 00:10:04,503 --> 00:10:07,199 but the hellbender doesn't give up easily. 76 00:10:12,812 --> 00:10:17,181 Both animals try to keep out of the current and habitually creep into crevices. 77 00:10:29,795 --> 00:10:32,628 But that sometimes is a mistake. 78 00:10:54,987 --> 00:10:59,014 Streams that tumble down the sides of the valleys and feed young rivers 79 00:10:59,191 --> 00:11:00,920 have their own population. 80 00:11:03,062 --> 00:11:09,228 In Malaysia, the big-headed turtle clambers around the waterfalls, using its tail as a prop. 81 00:11:20,546 --> 00:11:26,143 In West African waterfalls, and nowhere else, lives the extraordinary hairy frog. 82 00:11:29,588 --> 00:11:34,321 Its so-called hairs are filaments of skin on its flanks which act as gills, 83 00:11:34,694 --> 00:11:37,356 helping it to absorb oxygen from the water. 84 00:11:39,765 --> 00:11:45,362 And, almost as unusual, it has claws that help it grip the slippery stones 85 00:12:01,687 --> 00:12:07,421 The many sources of the Amazon began as rivulets on the eastern flanks of the Andes. 86 00:12:07,593 --> 00:12:14,761 Now, 5,000 feet lower down, each has grown beyond recognition and cut its own zigzag valley. 87 00:12:15,334 --> 00:12:20,601 White water, tumbling down the valley wall, joins the brown water of a larger tributary, 88 00:12:20,773 --> 00:12:23,105 heavy with mud and sediment. 89 00:12:27,413 --> 00:12:33,613 And as it gets bigger and bigger, so it becomes more and more powerful. 90 00:12:33,986 --> 00:12:38,082 It's the dry season at the moment and the river is comparatively low. 91 00:12:38,324 --> 00:12:42,920 But during the rains, when it's in spate, its waters rise up over here 92 00:12:43,095 --> 00:12:50,001 and the sheer volume and weight and force of them can shift boulders the size of these. 93 00:13:05,117 --> 00:13:11,386 The volume and speed of its waters are not the river's only weapons. 94 00:13:12,224 --> 00:13:14,852 It also has teeth. 95 00:13:15,528 --> 00:13:20,090 And in this empty rainy-season part of its bed, you can see them. 96 00:13:23,936 --> 00:13:30,466 Sand and gravel, fragments of rock that have been eroded from higher up in its course 97 00:13:30,709 --> 00:13:36,375 and which the river hurls with enormous force at the rocks of its river bed. 98 00:13:40,085 --> 00:13:44,681 With such tools, it can carve away the sides of mountains. 99 00:13:59,071 --> 00:14:03,599 Young, vigorous rivers transform the land, demolishing the mountains, 100 00:14:03,809 --> 00:14:09,111 breaking down the debris into smaller particles and carrying them away downstream. 101 00:14:09,915 --> 00:14:15,979 This river in China is perpetually so turbid that it's called the Huang Ho, the Yellow River. 102 00:14:16,288 --> 00:14:19,985 It carries a bigger load of sediment than any river in the world. 103 00:14:20,793 --> 00:14:28,290 During floods, each cubic yard of water contains over 2,000 pounds of soil and pulverised rock. 104 00:14:40,980 --> 00:14:44,848 Rivers in the full vigour of their youth are terrifyingly strong. 105 00:14:45,184 --> 00:14:47,709 They roll great boulders along their beds, 106 00:14:47,887 --> 00:14:53,553 they cut away at the banks, undermining trees which crash into the waters and are swept away. 107 00:15:02,635 --> 00:15:08,232 When a river encounters a band of unusually hard rock, such as an ancient flow of basalt lava, 108 00:15:08,407 --> 00:15:10,875 its progress is temporarily slowed. 109 00:15:11,277 --> 00:15:15,373 It spreads out across the barrier and then tumbles over the front edge. 110 00:15:16,015 --> 00:15:19,451 So are formed some of the loveliest cascades. 111 00:15:19,885 --> 00:15:24,481 These are the falls of Iguacu on the border of Brazil and Paraguay. 112 00:15:24,857 --> 00:15:27,189 They can't compare in height with the Angel Falls, 113 00:15:27,359 --> 00:15:32,422 but in terms of the volume of water that passes over them, they are incomparably bigger. 114 00:15:45,311 --> 00:15:48,246 The falling waters pound away at the base of the falls, 115 00:15:48,414 --> 00:15:52,441 undercutting the basalt until blocks split off the face. 116 00:15:52,918 --> 00:15:58,220 So the falls steadily work their way upriver, leaving downstream a deep gorge, 117 00:15:58,424 --> 00:16:03,123 and animals live even here, within the falls themselves. 118 00:16:05,731 --> 00:16:09,667 Swifts perch on the rock face behind the cascade. 119 00:16:10,803 --> 00:16:13,363 Every evening they congregate high above Iguacu. 120 00:16:13,539 --> 00:16:17,168 After a day of hawking for insects, they're ready to roost. 121 00:16:18,377 --> 00:16:21,869 And where safer than behind a screen of falling water? 122 00:16:25,117 --> 00:16:29,611 Some dive down with such speed that they shoot right through the fall. 123 00:16:43,635 --> 00:16:47,093 And now the river has left the mountains far behind 124 00:16:47,272 --> 00:16:49,604 and has changed its character considerably. 125 00:16:49,942 --> 00:16:54,538 It's bigger, it's broader, and its waters carry not only sand and gravel 126 00:16:54,713 --> 00:16:59,116 but rich nutrients washed in from its vegetation-covered banks. 127 00:16:59,418 --> 00:17:04,879 And after it's gone over its last rapids and tumbled over its last fall, 128 00:17:05,057 --> 00:17:08,026 it becomes a very different river indeed. 129 00:17:14,600 --> 00:17:21,096 It's middle-aged: Ampler, less violent, more sluggish and richer. 130 00:17:24,610 --> 00:17:28,171 On the banks of the Amazon tributaries, the jungle stands thick. 131 00:17:29,148 --> 00:17:33,209 Birds like the sun bittern stalk quietly in search of a meal. 132 00:17:35,220 --> 00:17:38,246 Huge fish cruise through the slow waters. 133 00:17:41,727 --> 00:17:47,165 The arapaima, one of the largest of freshwater fish, grows over six feet long. 134 00:17:47,766 --> 00:17:54,604 The Amazon contains over 3,000 different kinds of fish. That's more than live in all the Atlantic 135 00:17:58,977 --> 00:18:01,673 Rays almost certainly evolved in the sea, 136 00:18:01,914 --> 00:18:07,147 but this species has managed to make the change to fresh water and lives high up the Amazon. 137 00:18:08,387 --> 00:18:11,015 Many fish have evolved here in fresh water 138 00:18:11,190 --> 00:18:16,753 and become suited to all its variations of depth, speed and chemical composition, 139 00:18:17,029 --> 00:18:23,059 to muddy water and to clear, to stretches that are thick with plants and places where there are none. 140 00:18:23,569 --> 00:18:25,696 Their variety is enormous. 141 00:18:28,140 --> 00:18:31,940 Take, for example, just one family: The catfish. 142 00:18:32,644 --> 00:18:38,105 They're bottom-dwelling fish, with feelers on their snouts that have sense organs on them, 143 00:18:38,350 --> 00:18:43,151 so the fish can feel and taste their way through the thick, muddy water or at night. 144 00:18:44,857 --> 00:18:46,654 There are small ones and immense ones, 145 00:18:46,825 --> 00:18:50,454 some that give electric shocks and others that swim upside down. 146 00:18:50,796 --> 00:18:53,356 Those in fast-flowing waters 147 00:18:53,532 --> 00:18:58,026 have suckers on their chins or undersides with which they cling to rocks. 148 00:18:59,838 --> 00:19:07,074 In South America alone, there are 1,200 different species of catfish. 149 00:19:33,672 --> 00:19:37,972 In these crowded waters, many fish give special protection to their young 150 00:19:38,143 --> 00:19:40,202 for the first few weeks of their lives. 151 00:19:40,546 --> 00:19:43,879 This fish, the discus, goes even further. 152 00:19:44,116 --> 00:19:46,914 It provides its fry with special food. 153 00:19:47,452 --> 00:19:51,320 The parents exude a nutritious slime from their skin 154 00:19:51,490 --> 00:19:55,688 and the young graze over their flanks, feeding on it. 155 00:20:29,328 --> 00:20:33,731 After a week, they're big enough to feed on small particles floating in the water. 156 00:20:46,578 --> 00:20:52,414 These are now a month old and have already assumed the disc-like shape of their parents. 157 00:20:52,718 --> 00:20:57,678 They're becoming independent, but they've strayed past the lair of an electric e 158 00:21:00,959 --> 00:21:02,551 The eel has poor eyesight, 159 00:21:02,728 --> 00:21:07,825 but it detects the presence of objects around it with short electric discharges, a kind of radar. 160 00:21:10,235 --> 00:21:16,003 It rises for a gulp of air. This time the young discus seem to have escaped detection. 161 00:21:24,283 --> 00:21:29,050 But the eel can also produce a major electric shock which stuns its prey. 162 00:21:44,403 --> 00:21:49,170 It releases its capture. Perhaps so small a fish is not worth eating. 163 00:21:49,408 --> 00:21:54,539 The young discus, apart from the marks of the eel's jaws on its flanks, seems no worse off. 164 00:21:56,448 --> 00:22:00,885 One Amazonian fish puts its eggs beyond the reach of any water-living predator: 165 00:22:01,119 --> 00:22:03,178 On leaves overhanging a river. 166 00:22:05,157 --> 00:22:07,751 A pair of splashing tetras are courting. 167 00:22:10,195 --> 00:22:13,995 They curve their bodies and, for an instant, leap clear of the water. 168 00:22:16,034 --> 00:22:18,628 Sometimes a third fish joins in. 169 00:22:24,343 --> 00:22:26,174 The bigger of the two is the male. 170 00:22:27,779 --> 00:22:32,409 For a moment the pair hang on the leaf, supported by the suction of the male's floppy fins 171 00:22:35,987 --> 00:22:42,051 Again and again, they jump. In this one moment, the female lays her eggs and drops off, 172 00:22:42,227 --> 00:22:44,821 and the male fertilises them and follows her. 173 00:22:45,630 --> 00:22:48,531 Each time, they leave behind a dozen or so eggs. 174 00:22:55,574 --> 00:22:59,101 A few infertile eggs drop off, but they're not wasted. 175 00:22:59,311 --> 00:23:03,213 Eventually as many as 200 eggs are safely placed out of harm's way, 176 00:23:03,415 --> 00:23:07,283 and the river can be an exceedingly dangerous place. 177 00:23:08,720 --> 00:23:12,053 Piranha, the most savage of all the Amazon's fish. 178 00:23:12,324 --> 00:23:18,024 A swimming capybara suddenly realises their presence and tries to retreat, but it's too late. 179 00:23:23,902 --> 00:23:27,360 The splashing, the taste of blood spreading through the water, 180 00:23:27,539 --> 00:23:33,535 attracts more of the shoal until there are hundreds, all possessed by a frenzy for flesh. 181 00:23:33,745 --> 00:23:39,377 None are much more than a foot long, but their teeth are sharp enough to cut clean through bone. 182 00:23:48,460 --> 00:23:50,792 Within minutes, there's little left. 183 00:23:54,499 --> 00:24:00,438 As the river gets older, it slows down. A minor obstacle in its path is now enough to deflect it. 184 00:24:00,605 --> 00:24:06,942 The water flowing round the outside of a bend speeds up and cuts away at the bank. 185 00:24:07,179 --> 00:24:09,443 On the inside, where the current is slow, 186 00:24:09,614 --> 00:24:14,017 the water drops its load of sediment to form a shoal. 187 00:24:14,186 --> 00:24:19,715 So the bend becomes more exaggerated as the elderly river swings from side to side 188 00:24:19,891 --> 00:24:22,223 in a series of loops and meanders. 189 00:24:22,928 --> 00:24:28,867 One bend may approach another until the neck of land between them is so narrow it collapses. 190 00:24:29,100 --> 00:24:34,766 Then the river takes the shorter course and the meander is left isolated as a curving lake 191 00:24:35,574 --> 00:24:38,236 There the water, at last, is still. 192 00:24:38,710 --> 00:24:43,841 Plants no longer have to fight against a current, and the lakes become clogged with vegetation. 193 00:24:45,750 --> 00:24:52,451 These are the largest floating leaves of all, the leaves of the famous giant Amazon lily. 194 00:24:53,558 --> 00:24:57,221 Covering the water with leaves of this size is very aggressive, 195 00:24:57,395 --> 00:25:02,594 for it cuts out the light below, making it difficult for other plants to grow there 196 00:25:02,834 --> 00:25:09,398 The upturned rims of the great pads, as they grow, thrust to one side all other floating plants 197 00:25:10,141 --> 00:25:14,168 To prevent these leaves being destroyed by being eaten by fish, 198 00:25:14,346 --> 00:25:19,215 they are protected with very effective and ferocious spines underneath, 199 00:25:19,384 --> 00:25:22,581 as you can see most clearly on this half-opened bud. 200 00:25:24,256 --> 00:25:30,126 It can develop from the size of a soup plate to a huge emerald disc six feet across in a few days, 201 00:25:30,362 --> 00:25:33,229 growing at a rate of one square inch a minute. 202 00:25:33,765 --> 00:25:35,699 The flowers grow with similar speed. 203 00:25:35,967 --> 00:25:41,997 Each opens first in the evening and remains with its petals spread and fragrant all night. 204 00:25:42,207 --> 00:25:48,271 By the morning, however, it's closed again. But during the night it's taken prisoners. 205 00:25:49,047 --> 00:25:52,141 Inside the flower are beetles. 206 00:25:53,318 --> 00:25:57,049 Sometimes there are as many as 40 of them in a single bloom. 207 00:25:57,222 --> 00:26:04,094 They're not there just by accident. They've been attracted by sugary outgrowths in the centre. 208 00:26:04,429 --> 00:26:07,796 While they're trapped in there, they will feed on those. 209 00:26:07,966 --> 00:26:12,630 This evening the flower will open again, the beetles will be released 210 00:26:12,804 --> 00:26:18,470 and they'll fly off carrying pollen to cross-pollinate another lily flower. 211 00:26:18,643 --> 00:26:26,846 And then, afterjust two nights, this bloom, by now turned purple, will crumple and die. 212 00:26:30,689 --> 00:26:36,628 The leaves, strengthened by air-filled ribs beneath, can support the weight of a small child, 213 00:26:36,828 --> 00:26:40,764 and water birds can walk over them with complete confidence and safety. 214 00:26:45,203 --> 00:26:50,140 The jacana has greatly elongated toes that can spread its weight so effectively 215 00:26:50,308 --> 00:26:55,268 that it can tread on very flimsy leaves without submerging them. 216 00:26:55,647 --> 00:26:58,673 It seeks insects, and there are plenty to choose from. 217 00:26:59,551 --> 00:27:03,783 The pond skater sits on a leaf, but it could sit on the water, 218 00:27:03,989 --> 00:27:08,153 for the surface forms a platform that supports many small creatures. 219 00:27:08,727 --> 00:27:12,254 Water molecules are bound by a force akin to magnetism. 220 00:27:12,430 --> 00:27:18,858 They're not attracted to molecules of air above, so their forces are concentrated sideways, 221 00:27:19,137 --> 00:27:24,575 giving the surface a specially strong tension, and the pond skater hunts on it. 222 00:27:27,145 --> 00:27:28,976 It's lost its prey under the leaf. 223 00:27:32,951 --> 00:27:38,014 This time there is no escape. The pond skater stabs its victim and sucks it dry. 224 00:27:39,157 --> 00:27:42,923 It's crucially important for the pond skater to keep meticulously clean. 225 00:27:43,094 --> 00:27:47,463 The waxy surface of its body and the hairs on its feet repel water, 226 00:27:47,666 --> 00:27:52,103 but any dirt on them that is wettable would break the surface-tension film. 227 00:27:53,938 --> 00:27:58,432 They're aggressive insects, each with its own territory among the lily pads. 228 00:28:01,746 --> 00:28:06,410 Intruders are immediately chased away, and fights between rivals are common. 229 00:28:11,322 --> 00:28:16,624 The surface-tension film is not only the pond skaters' platform, but their sounding board. 230 00:28:16,861 --> 00:28:23,562 Through sense organs on their feet, they detect vibrations caused by the struggles of an insect, 231 00:28:23,768 --> 00:28:26,828 and by bouncing up and down they communicate, 232 00:28:27,005 --> 00:28:32,375 sending keep-out signals to rivals and come-hither signals to potential mates. 233 00:28:47,192 --> 00:28:51,424 Whirligig beetles use vibrations of the surface fi in a different way. 234 00:28:51,863 --> 00:28:56,197 They create ripples, and by monitoring the returning echoes, 235 00:28:56,367 --> 00:28:59,859 they detect the presence of other creatures and obstacles around them. 236 00:29:04,843 --> 00:29:09,678 They have excellent eyes, partitioned so that the lower half peers down 237 00:29:09,848 --> 00:29:11,873 to see what's happening in the water beneath. 238 00:29:13,518 --> 00:29:16,453 Hanging from below the surface is another hunter. 239 00:29:16,721 --> 00:29:22,682 Its tail has two tubes which penetrate the surface film and collect air so that it can breathe. 240 00:29:22,894 --> 00:29:27,490 At its other end, its head has ferocious jaws with which it seizes its prey. 241 00:29:27,665 --> 00:29:31,863 This is the larva of the giant diving beetle, and it's caught a tadpole. 242 00:29:34,305 --> 00:29:38,241 It has to come to the surface, even when it's adult, so it can collect air 243 00:29:38,409 --> 00:29:42,140 to sustain it on its hunting forays down into deeper waters. 244 00:29:45,650 --> 00:29:52,146 The water boatman patrols the surface not from above, like the pond skater, but from below. 245 00:29:52,791 --> 00:29:58,923 The two kinds of insects manage to collect most of the creatures trapped in the surface film. 246 00:29:59,831 --> 00:30:02,823 The camphor beetle lives on plants at the water's edge, 247 00:30:03,034 --> 00:30:06,333 but it is perhaps the most versatile of all water-walkers. 248 00:30:07,438 --> 00:30:10,032 It can run over water, like a pond skater. 249 00:30:12,143 --> 00:30:17,672 It can also produce a substance which reduces the tension between water molecules. 250 00:30:17,916 --> 00:30:23,821 In emergencies it squirts this from its tail, and with the tension pulling hard at the front, 251 00:30:24,255 --> 00:30:29,352 it shoots across the surface so fast that the only way to see it clearly is in slow motion. 252 00:30:33,464 --> 00:30:39,494 And, as a final demonstration of its versatility, it can, like most good beetles, fly. 253 00:30:42,307 --> 00:30:47,267 One particularly ferocious hunter lives on the edge of lakes and ponds in Europe, 254 00:30:47,612 --> 00:30:48,874 the fishing spider. 255 00:30:50,348 --> 00:30:55,251 It uses the surface-tension film in the same way as other spiders use their webs. 256 00:30:55,620 --> 00:31:01,559 With its front legs resting delicately on the surface, it feels for tell-tale vibrations. 257 00:31:05,496 --> 00:31:10,365 But it also has excellent sight and can see potential prey below the surface. 258 00:31:13,638 --> 00:31:16,539 The stickleback sees only the spider's feet. 259 00:31:26,217 --> 00:31:29,015 That is a greatly slowed-down version of the kill. 260 00:31:29,187 --> 00:31:31,553 In reality, the pounce is rapier-swift 261 00:31:31,723 --> 00:31:35,955 and the stickleback had little chance once it strayed within range. 262 00:31:59,817 --> 00:32:05,847 The lakes and ponds fed by streams or cut off from the main river are comparatively small. 263 00:32:06,124 --> 00:32:09,992 But where rivers flow into basins created by geological faults, 264 00:32:10,228 --> 00:32:12,890 their water accumulates in immense lakes. 265 00:32:13,765 --> 00:32:19,328 This is Lake Prespa in Yugoslavia. Not the largest of lakes but, even so, 20 miles long. 266 00:32:19,704 --> 00:32:25,199 As the rivers enter its still waters, they lose their impetus and drop their sediment, 267 00:32:25,543 --> 00:32:29,479 so such lakes are potentially fertile, and their animal inhabitants, 268 00:32:29,647 --> 00:32:35,108 no longer harassed by a current nor hemmed in by a shallow bottom or banks, 269 00:32:35,353 --> 00:32:37,218 can proliferate, and they do. 270 00:32:37,855 --> 00:32:40,016 Fish swarm in their waters. 271 00:32:47,098 --> 00:32:52,161 And fish-eating birds, like pelicans and cormorants, swarm correspondingly. 272 00:33:08,753 --> 00:33:12,018 Land-based creatures haunt its margins. 273 00:33:12,256 --> 00:33:16,716 These may be its most fertile parts, for the lack of strong currents in a deep lake 274 00:33:16,894 --> 00:33:19,556 can leave the bottom starved of oxygen, 275 00:33:19,998 --> 00:33:25,698 but in the shallows, especially when warmed by the sun, algae and other plants flourish, 276 00:33:25,903 --> 00:33:31,170 small invertebrates proliferate and there's food for even the least agile of hunters. 277 00:33:56,000 --> 00:33:59,128 But in one way these large lakes are very special. 278 00:33:59,437 --> 00:34:03,806 This trout, with distinctive red spots, lives in Lake Ohrid, 279 00:34:03,975 --> 00:34:07,604 a few miles away from Lake Prespa, but nowhere else in the world. 280 00:34:08,212 --> 00:34:12,046 Isolated in the lake, communities of fish become very inbred. 281 00:34:12,250 --> 00:34:19,247 Small characteristics that could be lost become fixed, and the fish evolve into new species. 282 00:34:21,192 --> 00:34:23,854 A similar thing has happened to the shrimps. 283 00:34:30,935 --> 00:34:37,306 And among the many different species of water snails, several are now unique to Lake Ohrid. 284 00:34:42,513 --> 00:34:47,917 In the heart of Russia lies a stretch of fresh wat so huge and so ancient 285 00:34:48,086 --> 00:34:54,252 that these processes have produced new species on a scale unequalled anywhere else in the world, 286 00:34:54,926 --> 00:34:56,484 Lake Baikal. 287 00:34:59,030 --> 00:35:03,797 The lake lies in a great depression formed by faulting in the earth's crust. 288 00:35:03,968 --> 00:35:10,703 It's 400 miles long and 5,000 feet deep, the deepest of all lakes. 289 00:35:13,611 --> 00:35:19,243 In the depths of the lake, 1,000 feet down, lives a unique kind of salmon, the omul. 290 00:35:19,851 --> 00:35:25,187 In summer, they move up into the shallows and feed on caddis fly larvae and sand hoppers, 291 00:35:25,456 --> 00:35:29,392 and here they're caught in great numbers for their delicious eating. 292 00:35:40,037 --> 00:35:43,734 But this is only one of Baikal's special inhabitan 293 00:35:43,941 --> 00:35:50,312 Of the 1,200 different kinds of fish and other animals and 500 plants that it contains, 294 00:35:50,515 --> 00:35:52,574 over 80% are unique. 295 00:35:53,284 --> 00:35:58,847 There are unique molluscs, unique flatworms and even one unique mammal, the Baikal seal. 296 00:36:03,161 --> 00:36:08,895 This tiny seal is almost certainly descended from the ringed seal of the Arctic Sea. 297 00:36:09,233 --> 00:36:12,464 Today the lake is over 1,000 miles away from that sea. 298 00:36:12,837 --> 00:36:17,240 It's likely that their ancestors arrived during the Ice Age, 299 00:36:17,508 --> 00:36:20,341 when the journey may have been shorter and easier. 300 00:36:20,811 --> 00:36:25,748 Since then, cut off from other ringed seals, they've developed in their own way. 301 00:36:27,985 --> 00:36:30,977 The Amazon has no great lake on its course, 302 00:36:31,155 --> 00:36:35,751 so even in its middle stretches it still carries mud from the Andes. 303 00:36:36,327 --> 00:36:38,989 The Rio Negro, which joins it, is clear, 304 00:36:39,230 --> 00:36:42,996 for it has come from the north-west where the rocks are hard and bare. 305 00:36:43,534 --> 00:36:49,495 The two immense rivers flow for miles alongside one another in the same bed, scarcely mixing. 306 00:36:50,408 --> 00:36:53,935 As well as sediment, they also carry abundant nutrients, 307 00:36:54,145 --> 00:36:57,478 and life on their banks flourishes as never before 308 00:36:59,483 --> 00:37:04,511 Herds of capybara wade through the shallows, cropping the luxuriant plants. 309 00:37:10,761 --> 00:37:14,026 They're excellent swimmers, with webs between their toes, 310 00:37:14,232 --> 00:37:19,568 and they have that placing of eyes, ears and nostrils so valuable to mammals that swim, 311 00:37:19,770 --> 00:37:22,796 on top of the head, so as the animal lies submerged, 312 00:37:22,974 --> 00:37:27,308 they can see, hear and smell what's going on above water around them. 313 00:37:42,059 --> 00:37:44,323 Giant otters have a similar head design 314 00:37:44,562 --> 00:37:49,727 and sometimes lift themselves above the surface to get an even better view of their surroundings. 315 00:37:55,473 --> 00:38:01,901 This Amazonian species is the biggest of all otters, six feet long and a powerful swimmer. 316 00:38:02,346 --> 00:38:06,806 It's well-equipped with large, webbed feet, a flattened tail and sensitive whiskers. 317 00:38:07,351 --> 00:38:11,879 A pair lays claim to a stretch of river by making patches on the bank, 318 00:38:12,056 --> 00:38:14,650 marking them with their own personal smell. 319 00:38:26,871 --> 00:38:32,400 There are otters in many of the great rivers of th world and they are the most graceful of swimmers. 320 00:38:47,124 --> 00:38:51,220 In India they share the harvest of fish with the gavial. 321 00:38:51,462 --> 00:38:56,024 Most of the crocodile family, when adult, feed largely on carrion, 322 00:38:56,233 --> 00:39:01,865 but the gavial eats only fish, and has long, narrow jaws, studded with abundant teeth, 323 00:39:02,073 --> 00:39:04,064 with which it catches them underwater. 324 00:39:07,111 --> 00:39:09,978 A host of birds also claim a share of the river fi 325 00:39:10,548 --> 00:39:14,644 This is the hooded merganser, one of a group of ducks called sawbills. 326 00:39:23,961 --> 00:39:29,991 Its beak, like the gavial's jaws, is long and narr so it's easily snapped together underwater, 327 00:39:30,234 --> 00:39:34,500 and it also has a notched edge to give it a grip on the slippery fish. 328 00:39:38,109 --> 00:39:43,570 But their feathers trap so much air that the pair have to work very hard to get down to any depths. 329 00:39:45,082 --> 00:39:47,312 Coming up again is easy enough. 330 00:39:48,352 --> 00:39:52,311 But the meal was a mere mouthful, and the merganser must look for another one. 331 00:39:56,193 --> 00:39:59,287 And on the bottom lurks more danger for a fish. 332 00:40:00,064 --> 00:40:01,088 A worm, perhaps? 333 00:40:06,737 --> 00:40:09,604 No, the deceiving tongue of a turtle. 334 00:40:38,903 --> 00:40:42,999 And in the sky above the river, more trouble for a fish. 335 00:40:53,517 --> 00:40:55,212 The kingfisher. 336 00:41:19,243 --> 00:41:21,541 And there's still one left for next time. 337 00:41:24,615 --> 00:41:30,110 The fish eagle is not a diver but a pouncer, with a marvellously coordinated action. 338 00:41:34,692 --> 00:41:38,992 The aerial onslaught on the fish continues not only throughout the day but at night. 339 00:41:39,296 --> 00:41:42,129 An owl goes fishing in Africa. 340 00:41:47,371 --> 00:41:50,499 Its legs are bare. Feathers would drag in the water. 341 00:41:50,674 --> 00:41:55,702 And it has spines on the underside of its toes which give it a firm grasp on a fish. 342 00:42:28,779 --> 00:42:34,217 In the last phase of their lives, these great rivers often flow out of control. 343 00:42:34,718 --> 00:42:39,587 Their tributaries in the mountains, fed by the heavy storms of the rainy season, 344 00:42:39,757 --> 00:42:43,158 pour so much water into them that they burst their banks. 345 00:42:44,795 --> 00:42:50,028 The Amazon rises every year to flood tens of thousands of square miles of forest, 346 00:42:50,267 --> 00:42:53,065 in some parts as much as 40 feet deep. 347 00:42:59,410 --> 00:43:03,403 Some of these trees are flooded for eight to ten months every year. 348 00:43:03,681 --> 00:43:07,583 They need only a few months annually out of water for them to grow 349 00:43:07,751 --> 00:43:10,185 and for their seeds to sprout. 350 00:43:10,454 --> 00:43:13,048 We still don't know exactly how they manage it. 351 00:43:22,132 --> 00:43:26,967 As the floods well out over the land, fish from the river travel with them. 352 00:43:27,371 --> 00:43:31,171 This is going to be their best feeding time in the whole year. 353 00:43:35,946 --> 00:43:38,380 And so it is for other creatures too. 354 00:43:43,887 --> 00:43:48,654 Among the fallen tree leaves that carpet the bottom lies the mata-mata turtle, 355 00:43:48,826 --> 00:43:52,956 marvellously camouflaged, waiting for a decent-size fish. 356 00:44:08,545 --> 00:44:14,313 And there are plenty already here, sheltering, like the turtle, among the still unrotted leaves. 357 00:44:21,492 --> 00:44:24,928 Piranha are here too. These are not the flesh-eating kind. 358 00:44:25,162 --> 00:44:30,065 Their teeth are used for something different: Frui 359 00:44:47,851 --> 00:44:52,845 As the river becomes older and older, its riches increase still further. 360 00:44:56,026 --> 00:45:01,362 All over the world as rivers approach their end, they begin to deposit the sand and mud 361 00:45:01,532 --> 00:45:04,831 that they've gathered from so far and carried for so long. 362 00:45:05,102 --> 00:45:09,562 In many parts of the world reeds grow thickly on these shoals and banks, 363 00:45:09,740 --> 00:45:14,541 and their stems collect even more sediment as the river waters swirl through them. 364 00:45:15,646 --> 00:45:18,979 Living in these dense reed beds requires considerable skill. 365 00:45:19,349 --> 00:45:22,978 The little bittern is able to find its nest 366 00:45:23,153 --> 00:45:27,487 hidden out of sight somewhere in this seemingly uniform stretch of reeds. 367 00:45:30,894 --> 00:45:36,230 It regurgitates from its crop ample supplies of fish and frogs for its young. 368 00:45:48,378 --> 00:45:54,317 Their world is an infinity of vertical stems, but they're nimble climbers from an early age, 369 00:45:54,485 --> 00:45:57,147 and they leave the nest within a few days of hatching. 370 00:46:06,864 --> 00:46:12,029 There they wait, almost invisible, for their parents to return with restocked crops. 371 00:46:31,789 --> 00:46:35,885 The reed-clogged waters of a river delta are full of potential riches, 372 00:46:36,059 --> 00:46:38,789 not only for birds but for human beings. 373 00:46:39,296 --> 00:46:43,824 The reeds themselves are used for many purposes, but it's not an easy life here. 374 00:46:44,368 --> 00:46:47,030 Firm land on which to live is hard to find. 375 00:46:47,404 --> 00:46:52,535 In the Danube delta, the few solid sandbanks are tightly packed with dwellings. 376 00:46:52,843 --> 00:46:58,679 Earth has to be conserved with piles to prevent a slight change in the current washing it away. 377 00:46:59,249 --> 00:47:05,017 And there's the threat of a rise in the water leve caused not only by rainstorms upstream 378 00:47:05,189 --> 00:47:09,785 but an unusually high tide, backed by a storm sweeping up from the sea, 379 00:47:09,960 --> 00:47:12,360 which can cause devastating floods. 380 00:47:14,832 --> 00:47:18,632 In the twin joined deltas of the Tigris and Euphrates in Iraq, 381 00:47:18,836 --> 00:47:23,239 the marsh Arabs have become specialists in an amphibian life. 382 00:47:30,714 --> 00:47:34,013 Their houses seem to have solid enough foundations. 383 00:47:34,384 --> 00:47:38,480 In fact, they are floating on rafts of reeds. 384 00:47:54,905 --> 00:47:57,533 Some are the most elaborate constructions, 385 00:47:57,708 --> 00:48:03,874 yet all these soaring arches and roofs are also made from bundles of reeds. 386 00:48:04,481 --> 00:48:11,319 And reeds provide food for the livestock, so gathering them is a daily and never-ending chore. 387 00:48:26,236 --> 00:48:31,435 The herds have to be as much at home in the water are they are on their floating platforms 388 00:48:41,018 --> 00:48:44,010 The rewards of this precarious existence are, of course, 389 00:48:44,187 --> 00:48:48,749 the abundant fish which live all around the houses and even underneath them. 390 00:48:52,663 --> 00:48:58,260 So the fish and the marsh Arabs and the pelicans all flourish in one integrated community. 391 00:48:58,435 --> 00:49:02,462 The river has delivered the minerals it eroded from the mountains 392 00:49:02,639 --> 00:49:05,665 and the nutrients it collected from the forests. 393 00:49:06,243 --> 00:49:10,907 They sustain plants which are the food for small animals which are eaten by fish 394 00:49:11,081 --> 00:49:14,539 and which are gathered by great flocks of birds 395 00:49:14,718 --> 00:49:19,121 that, from the tropics to the Arctic, are the glories of the deltas. 396 00:49:25,595 --> 00:49:28,962 A blizzard of snow geese in northern Canada. 397 00:49:35,238 --> 00:49:40,540 Across the world in the tropics, on a delta in Papua New Guinea, magpie geese. 398 00:49:48,719 --> 00:49:51,916 In Australia, brolga cranes. 399 00:49:59,763 --> 00:50:02,596 Scarlet ibis in Venezuela. 400 00:50:04,801 --> 00:50:10,433 Plovers on almost any delta in the world. And, equally widespread, stilts. 401 00:50:26,223 --> 00:50:28,589 Flamingos in Africa. 402 00:50:38,001 --> 00:50:39,593 And spoonbills. 403 00:50:46,843 --> 00:50:51,644 Of all the deltas in the world, none is greater than that of the Amazon. 404 00:51:00,157 --> 00:51:02,523 For hundreds of miles along its lower course, 405 00:51:02,726 --> 00:51:07,823 the river has been so broad that it has been impossible to see from one side to another. 406 00:51:08,331 --> 00:51:13,598 Now, instead of receiving more tributaries, it splits into a tangle of separate channels. 407 00:51:16,440 --> 00:51:21,901 And on the last firm land on its banks stands a great and thriving port, 408 00:51:22,412 --> 00:51:26,143 for the river is so wide and deep that cargo ships from overseas 409 00:51:26,316 --> 00:51:32,778 can use it as a highway that can take them for 1,000 miles into the heart of South America. 410 00:51:34,658 --> 00:51:37,991 The Amazon's vital statistics are astounding. 411 00:51:38,261 --> 00:51:44,291 At any one time, two thirds of all the river water in the world is flowing between its banks. 412 00:51:44,601 --> 00:51:50,631 Here at its mouth, at Belem, it's 200 miles across a maze of channels and islands, 413 00:51:50,907 --> 00:51:54,741 one of which is, alone, bigger than the whole of Switzerland. 414 00:51:54,911 --> 00:52:01,248 The river maintains its identity far into the sea. It was because of this that it was discovered. 415 00:52:01,418 --> 00:52:06,355 In 1499 a Spanish sea captain, sailing well beyond the sight of land, 416 00:52:06,523 --> 00:52:11,654 suddenly became aware that the water he was crossing was fresh and not salty. 417 00:52:11,862 --> 00:52:15,389 He turned west and discovered this immense river. 418 00:52:15,632 --> 00:52:20,160 Indeed, it's not until 100 miles beyond the edge of the continent 419 00:52:20,337 --> 00:52:26,537 that particles of water which fell on the Andes complete their 4,000-mile-long journey 420 00:52:26,710 --> 00:52:30,146 and mingle with the salt water of the ocean. 421 00:52:35,185 --> 00:52:41,146 But along the coast, where the thrust of the river flood is not so great, is a halfway house. 422 00:52:41,625 --> 00:52:45,493 Here the water is neither fresh nor salt, but brackish. 423 00:52:45,729 --> 00:52:49,096 It's neither land nor sea, but banks of mud and sand 424 00:52:49,266 --> 00:52:52,929 that are half the time submerged and half the time exposed. 425 00:52:53,170 --> 00:52:58,802 And that intermediate, ever-changing territory is where we will be next time.