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