1 00:00:57,340 --> 00:01:02,890 A strangely shaped mountain catching the clouds high above the jungles of Venezuela. 2 00:01:04,350 --> 00:01:08,900 Its summit rocks have been carved into a multitude of grotesque shapes. 3 00:01:09,190 --> 00:01:16,740 The sculptor, an agent that is continuously at work on much of the landscape of our planet: Rainwater. 4 00:01:19,280 --> 00:01:22,620 It washes over the rock, eroding it chemically. 5 00:01:23,000 --> 00:01:29,210 It permeates the cracks, freezes, and chips it off in flakes and splinters. 6 00:01:33,010 --> 00:01:36,510 As the water flows downwards, it starts on a long journey 7 00:01:36,680 --> 00:01:39,850 that will take it from the mountains to the sea, 8 00:01:40,010 --> 00:01:45,270 and here, with a leap of over 3,000 feet, the highest made by any river, 9 00:01:45,520 --> 00:01:47,850 it forms the Angel Falls. 10 00:02:02,410 --> 00:02:06,210 Our journey begins not far from that towering waterfall 11 00:02:06,410 --> 00:02:12,460 on the high moorlands of Peru, 15,000 feet above the sea. 12 00:02:24,720 --> 00:02:29,770 Water is a very extraordinary and very precious substance, 13 00:02:29,940 --> 00:02:33,270 the only one on earth, apart from mercury, 14 00:02:33,570 --> 00:02:36,610 which remains liquid at normal temperatures and pressures, 15 00:02:36,820 --> 00:02:42,870 so it's an essential part of the bodies of all living organisms, animals and plant. 16 00:02:43,120 --> 00:02:46,160 Without it, life would come to an end. 17 00:02:46,830 --> 00:02:50,420 But this particular water is a very rare kind. 18 00:02:50,670 --> 00:02:54,500 97% of the water on earth is salty, the sea, 19 00:02:54,800 --> 00:02:59,340 but this was distilled from the surface of the sea by the heat of the sun, 20 00:02:59,550 --> 00:03:05,970 rose into the sky as vapour, condensed to form clouds and then fell again as rain and snow 21 00:03:06,180 --> 00:03:11,400 to form streams of pure, fresh, sweet water. 22 00:03:11,770 --> 00:03:18,320 But this particular stream is on its way to the sea a very long way away, 23 00:03:18,490 --> 00:03:23,280 because these are the Andes, and this is one of the many streams 24 00:03:23,450 --> 00:03:29,200 that can claim to be a source of the biggest river on earth, the Amazon. 25 00:03:32,620 --> 00:03:37,250 The difficulties of living in this young and violent river are formidable. 26 00:03:37,630 --> 00:03:42,930 Its waters are thick with powdered rock and mud, but they have gathered few nutrients, 27 00:03:43,300 --> 00:03:46,560 and they rush down the valley at tremendous speed. 28 00:03:46,930 --> 00:03:50,890 Anything that lives here has to be a prodigious swimmer. 29 00:03:51,560 --> 00:03:54,480 And these are. They're torrent ducks. 30 00:04:09,660 --> 00:04:13,120 They exploit the swirls and eddies with consummate skill, 31 00:04:13,330 --> 00:04:16,460 paddling with strokes of their large webbed feet. 32 00:04:16,710 --> 00:04:22,300 They head upstream, bracing themselves against rocks with their stiff quilled tail, 33 00:04:22,470 --> 00:04:27,470 and using small horny spurs on the wrists of their wings to give them purchase. 34 00:04:33,480 --> 00:04:39,110 A pair owns a stretch of the river, working their way up it to the frontier of their territory 35 00:04:39,270 --> 00:04:44,860 when they abandon themselves to the flood and are swept downstream to begin again. 36 00:05:01,000 --> 00:05:04,470 Anchored firmly to the rocks is a kind of moss. 37 00:05:06,760 --> 00:05:13,270 Mosses are primitive, ancient plants that appeared on earth long before flowering plants. 38 00:05:13,430 --> 00:05:17,980 This torrent moss is found in young rivers and streams all over the world, 39 00:05:18,270 --> 00:05:22,820 and wherever it grows, whether in the Andes or here in Europe, 40 00:05:23,030 --> 00:05:27,030 it provides shelter for a multitude of insect larvae. 41 00:05:28,950 --> 00:05:33,950 In summer, these creatures are transformed and fly briefly above the river to mate, 42 00:05:34,200 --> 00:05:37,170 but most of their lives are spent underwater. 43 00:05:37,540 --> 00:05:39,960 Some are streamlined against the current. 44 00:05:41,210 --> 00:05:45,590 The caddis fly larvae live in protective tubes, the hollow stem of a reed, 45 00:05:45,800 --> 00:05:49,510 or a construction of bits of wood stuck together with silk. 46 00:05:54,020 --> 00:06:00,770 Some weight themselves down by building their shelters from heavy grains of sand. 47 00:06:06,820 --> 00:06:10,820 The larva of the blackfly holds on to a pebble with its back end, 48 00:06:11,030 --> 00:06:15,790 while it grabs at food particles that are swept past it with the antennae on its head. 49 00:06:17,620 --> 00:06:24,380 It grips the rock with a ring of hooks, but even if it loses its hold, all is not lost. 50 00:06:27,170 --> 00:06:31,850 It has a lifeline of silk which it has attached to its chosen pebble. 51 00:06:47,400 --> 00:06:50,910 Having hauled itself back, it now has to get a new grip. 52 00:06:51,070 --> 00:06:55,700 It spins a tiny pad of silk from a spinneret just beneath its mouth, 53 00:06:55,910 --> 00:06:58,370 then it fixes its hooks into that. 54 00:07:01,170 --> 00:07:05,550 The nets with which it collects its food are modified antennae, 55 00:07:05,750 --> 00:07:10,800 and the larva brushes off what they catch with alternate flicks of its mouthparts. 56 00:07:14,930 --> 00:07:17,520 Not all caddis larvae live in solid tubes. 57 00:07:17,770 --> 00:07:23,190 This one builds a construction that serves both as a home and a food-gathering device. 58 00:07:30,280 --> 00:07:35,580 It uses its silk to produce a funnel-shaped scaffold of criss-crossing threads. 59 00:07:46,670 --> 00:07:49,630 Undulating its body is a way of aiding its breathing, 60 00:07:49,880 --> 00:07:53,930 for the movement speeds the flow of oxygen-bearing water through the funnel. 61 00:07:56,930 --> 00:07:59,100 It holds on with the hooks at the back... 62 00:08:03,310 --> 00:08:07,770 ...leaving its jaws and front legs free to do the construction work. 63 00:08:35,840 --> 00:08:39,720 This blackfly larva wasn't saved by its lifeline. 64 00:09:05,960 --> 00:09:12,050 But the caddis fly larva itself, ferocious and art trapper though it is, is also at risk. 65 00:09:16,260 --> 00:09:17,930 The dipper relishes it. 66 00:09:21,560 --> 00:09:25,190 Dippers live both in the rivers of North America and Europe. 67 00:09:27,400 --> 00:09:32,360 Underwater, their swimming technique is quite different from the torrent ducks'. 68 00:09:33,070 --> 00:09:39,200 Its feet are not webbed like a duck's, so it propels itself with its wings, flying underwater. 69 00:09:58,140 --> 00:10:01,470 In similar cold, fast-flowing streams in North America 70 00:10:01,640 --> 00:10:05,140 lives a kind of giant newt, the hellbender. 71 00:10:05,640 --> 00:10:09,310 When it's young, it also, like a dipper, takes insect larvae, 72 00:10:09,610 --> 00:10:15,280 but it can grow to over two feet long, and then it seeks much bigger prey. 73 00:10:17,530 --> 00:10:20,200 A crayfish would suit it admirably. 74 00:10:24,160 --> 00:10:30,130 A narrow escape. The crayfish saved itself at the last moment by a convulsive snap of its tail, 75 00:10:30,330 --> 00:10:33,130 but the hellbender doesn't give up easily. 76 00:10:38,970 --> 00:10:43,560 Both animals try to keep out of the current and habitually creep into crevices. 77 00:10:56,690 --> 00:10:59,660 But that sometimes is a mistake. 78 00:11:22,970 --> 00:11:27,140 Streams that tumble down the sides of the valleys and feed young rivers 79 00:11:27,350 --> 00:11:29,140 have their own population. 80 00:11:31,400 --> 00:11:37,820 In Malaysia, the big-headed turtle clambers around the waterfalls, using its tail as a prop. 81 00:11:49,620 --> 00:11:55,460 In West African waterfalls, and nowhere else, lives the extraordinary hairy frog. 82 00:11:59,050 --> 00:12:03,970 Its so-called hairs are filaments of skin on its flanks which act as gills, 83 00:12:04,340 --> 00:12:07,140 helping it to absorb oxygen from the water. 84 00:12:09,640 --> 00:12:15,480 And, almost as unusual, it has claws that help it grip the slippery stones 85 00:12:32,500 --> 00:12:38,500 The many sources of the Amazon began as rivulets on the eastern flanks of the Andes. 86 00:12:38,670 --> 00:12:46,140 Now, 5,000 feet lower down, each has grown beyond recognition and cut its own zigzag valley. 87 00:12:46,720 --> 00:12:52,230 White water, tumbling down the valley wall, joins the brown water of a larger tributary, 88 00:12:52,390 --> 00:12:54,850 heavy with mud and sediment. 89 00:12:59,320 --> 00:13:05,780 And as it gets bigger and bigger, so it becomes more and more powerful. 90 00:13:06,200 --> 00:13:10,450 It's the dry season at the moment and the river is comparatively low. 91 00:13:10,700 --> 00:13:15,500 But during the rains, when it's in spate, its waters rise up over here 92 00:13:15,670 --> 00:13:22,880 and the sheer volume and weight and force of them can shift boulders the size of these. 93 00:13:38,650 --> 00:13:45,200 The volume and speed of its waters are not the river's only weapons. 94 00:13:46,070 --> 00:13:48,780 It also has teeth. 95 00:13:49,490 --> 00:13:54,250 And in this empty rainy-season part of its bed, you can see them. 96 00:13:58,250 --> 00:14:05,090 Sand and gravel, fragments of rock that have been eroded from higher up in its course 97 00:14:05,340 --> 00:14:11,220 and which the river hurls with enormous force at the rocks of its river bed. 98 00:14:15,100 --> 00:14:19,900 With such tools, it can carve away the sides of mountains. 99 00:14:34,910 --> 00:14:39,630 Young, vigorous rivers transform the land, demolishing the mountains, 100 00:14:39,830 --> 00:14:45,380 breaking down the debris into smaller particles and carrying them away downstream. 101 00:14:46,220 --> 00:14:52,510 This river in China is perpetually so turbid that it's called the Huang Ho, the Yellow River. 102 00:14:52,850 --> 00:14:56,730 It carries a bigger load of sediment than any river in the world. 103 00:14:57,560 --> 00:15:05,360 During floods, each cubic yard of water contains over 2,000 pounds of soil and pulverised rock. 104 00:15:18,580 --> 00:15:22,630 Rivers in the full vigour of their youth are terrifyingly strong. 105 00:15:23,000 --> 00:15:25,630 They roll great boulders along their beds, 106 00:15:25,800 --> 00:15:31,720 they cut away at the banks, undermining trees which crash into the waters and are swept away. 107 00:15:41,190 --> 00:15:47,030 When a river encounters a band of unusually hard rock, such as an ancient flow of basalt lava, 108 00:15:47,190 --> 00:15:49,780 its progress is temporarily slowed. 109 00:15:50,200 --> 00:15:54,450 It spreads out across the barrier and then tumbles over the front edge. 110 00:15:55,120 --> 00:15:58,700 So are formed some of the loveliest cascades. 111 00:15:59,160 --> 00:16:03,960 These are the falls of Iguacu on the border of Brazil and Paraguay. 112 00:16:04,330 --> 00:16:06,800 They can't compare in height with the Angel Falls, 113 00:16:06,960 --> 00:16:12,260 but in terms of the volume of water that passes over them, they are incomparably bigger. 114 00:16:25,690 --> 00:16:28,730 The falling waters pound away at the base of the falls, 115 00:16:28,900 --> 00:16:33,110 undercutting the basalt until blocks split off the face. 116 00:16:33,610 --> 00:16:39,160 So the falls steadily work their way upriver, leaving downstream a deep gorge, 117 00:16:39,370 --> 00:16:44,250 and animals live even here, within the falls themselves. 118 00:16:46,960 --> 00:16:51,090 Swifts perch on the rock face behind the cascade. 119 00:16:52,260 --> 00:16:54,930 Every evening they congregate high above Iguacu. 120 00:16:55,090 --> 00:16:58,890 After a day of hawking for insects, they're ready to roost. 121 00:17:00,140 --> 00:17:03,810 And where safer than behind a screen of falling water? 122 00:17:07,190 --> 00:17:11,860 Some dive down with such speed that they shoot right through the fall. 123 00:17:26,500 --> 00:17:30,090 And now the river has left the mountains far behind 124 00:17:30,300 --> 00:17:32,710 and has changed its character considerably. 125 00:17:33,090 --> 00:17:37,850 It's bigger, it's broader, and its waters carry not only sand and gravel 126 00:17:38,050 --> 00:17:42,640 but rich nutrients washed in from its vegetation-covered banks. 127 00:17:42,930 --> 00:17:48,650 And after it's gone over its last rapids and tumbled over its last fall, 128 00:17:48,810 --> 00:17:51,940 it becomes a very different river indeed. 129 00:17:58,780 --> 00:18:05,540 It's middle-aged: Ampler, less violent, more sluggish and richer. 130 00:18:09,210 --> 00:18:12,920 On the banks of the Amazon tributaries, the jungle stands thick. 131 00:18:13,960 --> 00:18:18,180 Birds like the sun bittern stalk quietly in search of a meal. 132 00:18:20,260 --> 00:18:23,430 Huge fish cruise through the slow waters. 133 00:18:27,060 --> 00:18:32,730 The arapaima, one of the largest of freshwater fish, grows over six feet long. 134 00:18:33,360 --> 00:18:40,490 The Amazon contains over 3,000 different kinds of fish. That's more than live in all the Atlantic 135 00:18:45,040 --> 00:18:47,870 Rays almost certainly evolved in the sea, 136 00:18:48,120 --> 00:18:53,590 but this species has managed to make the change to fresh water and lives high up the Amazon. 137 00:18:54,880 --> 00:18:57,590 Many fish have evolved here in fresh water 138 00:18:57,800 --> 00:19:03,600 and become suited to all its variations of depth, speed and chemical composition, 139 00:19:03,890 --> 00:19:10,150 to muddy water and to clear, to stretches that are thick with plants and places where there are none. 140 00:19:10,690 --> 00:19:12,900 Their variety is enormous. 141 00:19:15,480 --> 00:19:19,400 Take, for example, just one family: The catfish. 142 00:19:20,160 --> 00:19:25,870 They're bottom-dwelling fish, with feelers on their snouts that have sense organs on them, 143 00:19:26,120 --> 00:19:31,120 so the fish can feel and taste their way through the thick, muddy water or at night. 144 00:19:32,880 --> 00:19:34,750 There are small ones and immense ones, 145 00:19:34,960 --> 00:19:38,720 some that give electric shocks and others that swim upside down. 146 00:19:39,090 --> 00:19:41,760 Those in fast-flowing waters 147 00:19:41,930 --> 00:19:46,640 have suckers on their chins or undersides with which they cling to rocks. 148 00:19:48,520 --> 00:19:56,070 In South America alone, there are 1,200 different species of catfish. 149 00:20:23,800 --> 00:20:28,270 In these crowded waters, many fish give special protection to their young 150 00:20:28,470 --> 00:20:30,600 for the first few weeks of their lives. 151 00:20:30,980 --> 00:20:34,440 This fish, the discus, goes even further. 152 00:20:34,690 --> 00:20:37,610 It provides its fry with special food. 153 00:20:38,150 --> 00:20:42,200 The parents exude a nutritious slime from their skin 154 00:20:42,360 --> 00:20:46,740 and the young graze over their flanks, feeding on it. 155 00:21:21,820 --> 00:21:26,410 After a week, they're big enough to feed on small particles floating in the water. 156 00:21:39,800 --> 00:21:45,880 These are now a month old and have already assumed the disc-like shape of their parents. 157 00:21:46,220 --> 00:21:51,390 They're becoming independent, but they've strayed past the lair of an electric e 158 00:21:54,810 --> 00:21:56,480 The eel has poor eyesight, 159 00:21:56,650 --> 00:22:01,980 but it detects the presence of objects around it with short electric discharges, a kind of radar. 160 00:22:04,490 --> 00:22:10,490 It rises for a gulp of air. This time the young discus seem to have escaped detection. 161 00:22:19,130 --> 00:22:24,090 But the eel can also produce a major electric shock which stuns its prey. 162 00:22:40,110 --> 00:22:45,070 It releases its capture. Perhaps so small a fish is not worth eating. 163 00:22:45,320 --> 00:22:50,660 The young discus, apart from the marks of the eel's jaws on its flanks, seems no worse off. 164 00:22:52,660 --> 00:22:57,290 One Amazonian fish puts its eggs beyond the reach of any water-living predator: 165 00:22:57,540 --> 00:22:59,670 On leaves overhanging a river. 166 00:23:01,750 --> 00:23:04,460 A pair of splashing tetras are courting. 167 00:23:07,010 --> 00:23:10,970 They curve their bodies and, for an instant, leap clear of the water. 168 00:23:13,100 --> 00:23:15,810 Sometimes a third fish joins in. 169 00:23:21,770 --> 00:23:23,650 The bigger of the two is the male. 170 00:23:25,320 --> 00:23:30,160 For a moment the pair hang on the leaf, supported by the suction of the male's floppy fins 171 00:23:33,910 --> 00:23:40,210 Again and again, they jump. In this one moment, the female lays her eggs and drops off, 172 00:23:40,420 --> 00:23:43,130 and the male fertilises them and follows her. 173 00:23:43,960 --> 00:23:46,960 Each time, they leave behind a dozen or so eggs. 174 00:23:54,300 --> 00:23:58,020 A few infertile eggs drop off, but they're not wasted. 175 00:23:58,230 --> 00:24:02,270 Eventually as many as 200 eggs are safely placed out of harm's way, 176 00:24:02,480 --> 00:24:06,530 and the river can be an exceedingly dangerous place. 177 00:24:08,030 --> 00:24:11,490 Piranha, the most savage of all the Amazon's fish. 178 00:24:11,780 --> 00:24:17,740 A swimming capybara suddenly realises their presence and tries to retreat, but it's too late. 179 00:24:23,880 --> 00:24:27,460 The splashing, the taste of blood spreading through the water, 180 00:24:27,630 --> 00:24:33,890 attracts more of the shoal until there are hundreds, all possessed by a frenzy for flesh. 181 00:24:34,140 --> 00:24:39,980 None are much more than a foot long, but their teeth are sharp enough to cut clean through bone. 182 00:24:49,480 --> 00:24:51,900 Within minutes, there's little left. 183 00:24:55,740 --> 00:25:01,960 As the river gets older, it slows down. A minor obstacle in its path is now enough to deflect it. 184 00:25:02,120 --> 00:25:08,750 The water flowing round the outside of a bend speeds up and cuts away at the bank. 185 00:25:08,960 --> 00:25:11,340 On the inside, where the current is slow, 186 00:25:11,510 --> 00:25:16,090 the water drops its load of sediment to form a shoal. 187 00:25:16,300 --> 00:25:22,060 So the bend becomes more exaggerated as the elderly river swings from side to side 188 00:25:22,230 --> 00:25:24,690 in a series of loops and meanders. 189 00:25:25,400 --> 00:25:31,610 One bend may approach another until the neck of land between them is so narrow it collapses. 190 00:25:31,860 --> 00:25:37,740 Then the river takes the shorter course and the meander is left isolated as a curving lake 191 00:25:38,580 --> 00:25:41,370 There the water, at last, is still. 192 00:25:41,870 --> 00:25:47,210 Plants no longer have to fight against a current, and the lakes become clogged with vegetation. 193 00:25:49,210 --> 00:25:56,180 These are the largest floating leaves of all, the leaves of the famous giant Amazon lily. 194 00:25:57,340 --> 00:26:01,180 Covering the water with leaves of this size is very aggressive, 195 00:26:01,350 --> 00:26:06,770 for it cuts out the light below, making it difficult for other plants to grow there 196 00:26:07,020 --> 00:26:13,860 The upturned rims of the great pads, as they grow, thrust to one side all other floating plants 197 00:26:14,650 --> 00:26:18,820 To prevent these leaves being destroyed by being eaten by fish, 198 00:26:19,030 --> 00:26:24,080 they are protected with very effective and ferocious spines underneath, 199 00:26:24,290 --> 00:26:27,620 as you can see most clearly on this half-opened bud. 200 00:26:29,330 --> 00:26:35,470 It can develop from the size of a soup plate to a huge emerald disc six feet across in a few days, 201 00:26:35,720 --> 00:26:38,720 growing at a rate of one square inch a minute. 202 00:26:39,260 --> 00:26:41,260 The flowers grow with similar speed. 203 00:26:41,560 --> 00:26:47,850 Each opens first in the evening and remains with its petals spread and fragrant all night. 204 00:26:48,060 --> 00:26:54,400 By the morning, however, it's closed again. But during the night it's taken prisoners. 205 00:26:55,190 --> 00:26:58,450 Inside the flower are beetles. 206 00:26:59,660 --> 00:27:03,540 Sometimes there are as many as 40 of them in a single bloom. 207 00:27:03,740 --> 00:27:10,880 They're not there just by accident. They've been attracted by sugary outgrowths in the centre. 208 00:27:11,250 --> 00:27:14,760 While they're trapped in there, they will feed on those. 209 00:27:14,920 --> 00:27:19,800 This evening the flower will open again, the beetles will be released 210 00:27:19,970 --> 00:27:25,890 and they'll fly off carrying pollen to cross-pollinate another lily flower. 211 00:27:26,060 --> 00:27:34,610 And then, after just two nights, this bloom, by now turned purple, will crumple and die. 212 00:27:38,610 --> 00:27:44,830 The leaves, strengthened by air-filled ribs beneath, can support the weight of a small child, 213 00:27:45,040 --> 00:27:49,120 and water birds can walk over them with complete confidence and safety. 214 00:27:53,750 --> 00:27:58,920 The jacana has greatly elongated toes that can spread its weight so effectively 215 00:27:59,090 --> 00:28:04,260 that it can tread on very flimsy leaves without submerging them. 216 00:28:04,640 --> 00:28:07,810 It seeks insects, and there are plenty to choose from. 217 00:28:08,730 --> 00:28:13,150 The pond skater sits on a leaf, but it could sit on the water, 218 00:28:13,360 --> 00:28:17,690 for the surface forms a platform that supports many small creatures. 219 00:28:18,280 --> 00:28:21,950 Water molecules are bound by a force akin to magnetism. 220 00:28:22,160 --> 00:28:28,830 They're not attracted to molecules of air above, so their forces are concentrated sideways, 221 00:28:29,120 --> 00:28:34,790 giving the surface a specially strong tension, and the pond skater hunts on it. 222 00:28:37,500 --> 00:28:39,380 It's lost its prey under the leaf. 223 00:28:43,550 --> 00:28:48,810 This time there is no escape. The pond skater stabs its victim and sucks it dry. 224 00:28:50,020 --> 00:28:53,940 It's crucially important for the pond skater to keep meticulously clean. 225 00:28:54,100 --> 00:28:58,690 The waxy surface of its body and the hairs on its feet repel water, 226 00:28:58,900 --> 00:29:03,530 but any dirt on them that is wettable would break the surface-tension film. 227 00:29:05,410 --> 00:29:10,120 They're aggressive insects, each with its own territory among the lily pads. 228 00:29:13,580 --> 00:29:18,420 Intruders are immediately chased away, and fights between rivals are common. 229 00:29:23,550 --> 00:29:29,100 The surface-tension film is not only the pond skaters' platform, but their sounding board. 230 00:29:29,350 --> 00:29:36,310 Through sense organs on their feet, they detect vibrations caused by the struggles of an insect, 231 00:29:36,520 --> 00:29:39,730 and by bouncing up and down they communicate, 232 00:29:39,900 --> 00:29:45,490 sending keep-out signals to rivals and come-hither signals to potential mates. 233 00:30:00,960 --> 00:30:05,380 Whirligig beetles use vibrations of the surface film in a different way. 234 00:30:05,840 --> 00:30:10,350 They create ripples, and by monitoring the returning echoes, 235 00:30:10,510 --> 00:30:14,140 they detect the presence of other creatures and obstacles around them. 236 00:30:19,360 --> 00:30:24,400 They have excellent eyes, partitioned so that the lower half peers down 237 00:30:24,570 --> 00:30:26,700 to see what's happening in the water beneath. 238 00:30:28,410 --> 00:30:31,450 Hanging from below the surface is another hunter. 239 00:30:31,740 --> 00:30:37,960 Its tail has two tubes which penetrate the surface film and collect air so that it can breathe. 240 00:30:38,170 --> 00:30:42,960 At its other end, its head has ferocious jaws with which it seizes its prey. 241 00:30:43,170 --> 00:30:47,550 This is the larva of the giant diving beetle, and it's caught a tadpole. 242 00:30:50,100 --> 00:30:54,180 It has to come to the surface, even when it's adult, so it can collect air 243 00:30:54,350 --> 00:30:58,270 to sustain it on its hunting forays down into deeper waters. 244 00:31:01,900 --> 00:31:08,700 The water boatman patrols the surface not from above, like the pond skater, but from below. 245 00:31:09,360 --> 00:31:15,750 The two kinds of insects manage to collect most of the creatures trapped in the surface film. 246 00:31:16,710 --> 00:31:19,830 The camphor beetle lives on plants at the water's edge, 247 00:31:20,040 --> 00:31:23,460 but it is perhaps the most versatile of all water-walkers. 248 00:31:24,630 --> 00:31:27,340 It can run over water, like a pond skater. 249 00:31:29,550 --> 00:31:35,310 It can also produce a substance which reduces the tension between water molecules. 250 00:31:35,560 --> 00:31:41,730 In emergencies it squirts this from its tail, and with the tension pulling hard at the front, 251 00:31:42,150 --> 00:31:47,490 it shoots across the surface so fast that the only way to see it clearly is in slow motion. 252 00:31:51,780 --> 00:31:58,040 And, as a final demonstration of its versatility, it can, like most good beetles, fly. 253 00:32:01,000 --> 00:32:06,170 One particularly ferocious hunter lives on the edge of lakes and ponds in Europe, 254 00:32:06,510 --> 00:32:07,840 the fishing spider. 255 00:32:09,380 --> 00:32:14,470 It uses the surface-tension film in the same way as other spiders use their webs. 256 00:32:14,850 --> 00:32:21,060 With its front legs resting delicately on the surface, it feels for tell-tale vibrations. 257 00:32:25,150 --> 00:32:30,240 But it also has excellent sight and can see potential prey below the surface. 258 00:32:33,660 --> 00:32:36,660 The stickleback sees only the spider's feet. 259 00:32:46,750 --> 00:32:49,670 That is a greatly slowed-down version of the kill. 260 00:32:49,880 --> 00:32:52,340 In reality, the pounce is rapier-swift 261 00:32:52,510 --> 00:32:56,930 and the stickleback had little chance once it strayed within range. 262 00:33:21,790 --> 00:33:28,090 The lakes and ponds fed by streams or cut off from the main river are comparatively small. 263 00:33:28,380 --> 00:33:32,420 But where rivers flow into basins created by geological faults, 264 00:33:32,670 --> 00:33:35,430 their water accumulates in immense lakes. 265 00:33:36,350 --> 00:33:42,140 This is Lake Prespa in Yugoslavia. Not the largest of lakes but, even so, 20 miles long. 266 00:33:42,560 --> 00:33:48,270 As the rivers enter its still waters, they lose their impetus and drop their sediment, 267 00:33:48,650 --> 00:33:52,740 so such lakes are potentially fertile, and their animal inhabitants, 268 00:33:52,900 --> 00:33:58,620 no longer harassed by a current nor hemmed in by a shallow bottom or banks, 269 00:33:58,870 --> 00:34:00,790 can proliferate, and they do. 270 00:34:01,450 --> 00:34:03,710 Fish swarm in their waters. 271 00:34:11,090 --> 00:34:16,390 And fish-eating birds, like pelicans and cormorants, swarm correspondingly. 272 00:34:33,690 --> 00:34:37,070 Land-based creatures haunt its margins. 273 00:34:37,320 --> 00:34:41,990 These may be its most fertile parts, for the lack of strong currents in a deep lake 274 00:34:42,160 --> 00:34:44,960 can leave the bottom starved of oxygen, 275 00:34:45,410 --> 00:34:51,340 but in the shallows, especially when warmed by the sun, algae and other plants flourish, 276 00:34:51,590 --> 00:34:57,050 small invertebrates proliferate and there's food for even the least agile of hunters. 277 00:35:22,950 --> 00:35:26,210 But in one way these large lakes are very special. 278 00:35:26,540 --> 00:35:31,080 This trout, with distinctive red spots, lives in Lake Ohrid, 279 00:35:31,250 --> 00:35:35,050 a few miles away from Lake Prespa, but nowhere else in the world. 280 00:35:35,670 --> 00:35:39,680 Isolated in the lake, communities of fish become very inbred. 281 00:35:39,890 --> 00:35:47,180 Small characteristics that could be lost become fixed, and the fish evolve into new species. 282 00:35:49,230 --> 00:35:51,980 A similar thing has happened to the shrimps. 283 00:35:59,360 --> 00:36:06,040 And among the many different species of water snails, several are now unique to Lake Ohrid. 284 00:36:11,460 --> 00:36:17,090 In the heart of Russia lies a stretch of fresh water so huge and so ancient 285 00:36:17,260 --> 00:36:23,680 that these processes have produced new species on a scale unequalled anywhere else in the world, 286 00:36:24,390 --> 00:36:26,010 Lake Baikal. 287 00:36:28,680 --> 00:36:33,650 The lake lies in a great depression formed by faulting in the earth's crust. 288 00:36:33,810 --> 00:36:40,860 It's 400 miles long and 5,000 feet deep, the deepest of all lakes. 289 00:36:43,870 --> 00:36:49,750 In the depths of the lake, 1,000 feet down, lives a unique kind of salmon, the omul. 290 00:36:50,370 --> 00:36:55,960 In summer, they move up into the shallows and feed on caddis fly larvae and sand hoppers, 291 00:36:56,210 --> 00:37:00,340 and here they're caught in great numbers for their delicious eating. 292 00:37:11,440 --> 00:37:15,270 But this is only one of Baikal's special inhabitants. 293 00:37:15,520 --> 00:37:22,150 Of the 1,200 different kinds of fish and other animals and 500 plants that it contains, 294 00:37:22,360 --> 00:37:24,490 over 80% are unique. 295 00:37:25,240 --> 00:37:31,040 There are unique molluscs, unique flatworms and even one unique mammal, the Baikal seal. 296 00:37:35,540 --> 00:37:41,510 This tiny seal is almost certainly descended from the ringed seal of the Arctic Sea. 297 00:37:41,880 --> 00:37:45,260 Today the lake is over 1,000 miles away from that sea. 298 00:37:45,640 --> 00:37:50,220 It's likely that their ancestors arrived during the Ice Age, 299 00:37:50,520 --> 00:37:53,480 when the journey may have been shorter and easier. 300 00:37:53,940 --> 00:37:59,110 Since then, cut off from other ringed seals, they've developed in their own way. 301 00:38:01,440 --> 00:38:04,530 The Amazon has no great lake on its course, 302 00:38:04,740 --> 00:38:09,540 so even in its middle stretches it still carries mud from the Andes. 303 00:38:10,120 --> 00:38:12,910 The Rio Negro, which joins it, is clear, 304 00:38:13,160 --> 00:38:17,080 for it has come from the north-west where the rocks are hard and bare. 305 00:38:17,630 --> 00:38:23,840 The two immense rivers flow for miles alongside one another in the same bed, scarcely mixing. 306 00:38:24,800 --> 00:38:28,470 As well as sediment, they also carry abundant nutrients, 307 00:38:28,720 --> 00:38:32,180 and life on their banks flourishes as never before 308 00:38:34,270 --> 00:38:39,520 Herds of capybara wade through the shallows, cropping the luxuriant plants. 309 00:38:46,030 --> 00:38:49,450 They're excellent swimmers, with webs between their toes, 310 00:38:49,660 --> 00:38:55,210 and they have that placing of eyes, ears and nostrils so valuable to mammals that swim, 311 00:38:55,410 --> 00:38:58,580 on top of the head, so as the animal lies submerged, 312 00:38:58,750 --> 00:39:03,300 they can see, hear and smell what's going on above water around them. 313 00:39:18,650 --> 00:39:21,020 Giant otters have a similar head design 314 00:39:21,270 --> 00:39:26,650 and sometimes lift themselves above the surface to get an even better view of their surroundings. 315 00:39:32,660 --> 00:39:39,370 This Amazonian species is the biggest of all otters, six feet long and a powerful swimmer. 316 00:39:39,830 --> 00:39:44,460 It's well-equipped with large, webbed feet, a flattened tail and sensitive whiskers. 317 00:39:45,050 --> 00:39:49,760 A pair lays claim to a stretch of river by making patches on the bank, 318 00:39:49,930 --> 00:39:52,640 marking them with their own personal smell. 319 00:40:05,400 --> 00:40:11,160 There are otters in many of the great rivers of the world and they are the most graceful of swimmers. 320 00:40:26,510 --> 00:40:30,760 In India they share the harvest of fish with the gavial. 321 00:40:31,050 --> 00:40:35,810 Most of the crocodile family, when adult, feed largely on carrion, 322 00:40:36,010 --> 00:40:41,900 but the gavial eats only fish, and has long, narrow jaws, studded with abundant teeth, 323 00:40:42,100 --> 00:40:44,190 with which it catches them underwater. 324 00:40:47,360 --> 00:40:50,320 A host of birds also claim a share of the river fish. 325 00:40:50,950 --> 00:40:55,200 This is the hooded merganser, one of a group of ducks called sawbills. 326 00:41:04,920 --> 00:41:11,220 Its beak, like the gavial's jaws, is long and narrow so it's easily snapped together underwater, 327 00:41:11,470 --> 00:41:15,890 and it also has a notched edge to give it a grip on the slippery fish. 328 00:41:19,680 --> 00:41:25,360 But their feathers trap so much air that the pair have to work very hard to get down to any depths. 329 00:41:26,940 --> 00:41:29,280 Coming up again is easy enough. 330 00:41:30,360 --> 00:41:34,490 But the meal was a mere mouthful, and the merganser must look for another one. 331 00:41:38,540 --> 00:41:41,750 And on the bottom lurks more danger for a fish. 332 00:41:42,580 --> 00:41:43,620 A worm, perhaps? 333 00:41:49,510 --> 00:41:52,510 No, the deceiving tongue of a turtle. 334 00:42:23,080 --> 00:42:27,330 And in the sky above the river, more trouble for a fish. 335 00:42:38,300 --> 00:42:40,060 The kingfisher. 336 00:43:05,120 --> 00:43:07,540 And there's still one left for next time. 337 00:43:10,710 --> 00:43:16,470 The fish eagle is not a diver but a pouncer, with a marvellously coordinated action. 338 00:43:21,220 --> 00:43:25,730 The aerial onslaught on the fish continues not only throughout the day but at night. 339 00:43:26,020 --> 00:43:28,980 An owl goes fishing in Africa. 340 00:43:34,440 --> 00:43:37,700 Its legs are bare. Feathers would drag in the water. 341 00:43:37,910 --> 00:43:43,160 And it has spines on the underside of its toes which give it a firm grasp on a fish. 342 00:44:17,610 --> 00:44:23,280 In the last phase of their lives, these great rivers often flow out of control. 343 00:44:23,830 --> 00:44:28,910 Their tributaries in the mountains, fed by the heavy storms of the rainy season, 344 00:44:29,080 --> 00:44:32,630 pour so much water into them that they burst their banks. 345 00:44:34,340 --> 00:44:39,800 The Amazon rises every year to flood tens of thousands of square miles of forest, 346 00:44:40,050 --> 00:44:42,970 in some parts as much as 40 feet deep. 347 00:44:49,560 --> 00:44:53,730 Some of these trees are flooded for eight to ten months every year. 348 00:44:54,020 --> 00:44:58,110 They need only a few months annually out of water for them to grow 349 00:44:58,280 --> 00:45:00,820 and for their seeds to sprout. 350 00:45:01,070 --> 00:45:03,780 We still don't know exactly how they manage it. 351 00:45:13,250 --> 00:45:18,300 As the floods well out over the land, fish from the river travel with them. 352 00:45:18,710 --> 00:45:22,680 This is going to be their best feeding time in the whole year. 353 00:45:27,680 --> 00:45:30,180 And so it is for other creatures too. 354 00:45:35,940 --> 00:45:40,900 Among the fallen tree leaves that carpet the bottom lies the mata-mata turtle, 355 00:45:41,110 --> 00:45:45,410 marvellously camouflaged, waiting for a decent-size fish. 356 00:46:01,670 --> 00:46:07,680 And there are plenty already here, sheltering, like the turtle, among the still unrotted leaves. 357 00:46:15,150 --> 00:46:18,730 Piranha are here too. These are not the flesh-eating kind. 358 00:46:18,980 --> 00:46:24,110 Their teeth are used for something different, fruit. 359 00:46:42,630 --> 00:46:47,850 As the river becomes older and older, its riches increase still further. 360 00:46:51,180 --> 00:46:56,730 All over the world as rivers approach their end, they begin to deposit the sand and mud 361 00:46:56,900 --> 00:47:00,360 that they've gathered from so far and carried for so long. 362 00:47:00,650 --> 00:47:05,280 In many parts of the world reeds grow thickly on these shoals and banks, 363 00:47:05,490 --> 00:47:10,490 and their stems collect even more sediment as the river waters swirl through them. 364 00:47:11,620 --> 00:47:15,080 Living in these dense reed beds requires considerable skill. 365 00:47:15,500 --> 00:47:19,250 The little bittern is able to find its nest 366 00:47:19,460 --> 00:47:23,960 hidden out of sight somewhere in this seemingly uniform stretch of reeds. 367 00:47:27,510 --> 00:47:33,100 It regurgitates from its crop ample supplies of fish and frogs for its young. 368 00:47:45,740 --> 00:47:51,950 Their world is an infinity of vertical stems, but they're nimble climbers from an early age, 369 00:47:52,120 --> 00:47:54,910 and they leave the nest within a few days of hatching. 370 00:48:05,050 --> 00:48:10,430 There they wait, almost invisible, for their parents to return with restocked crops. 371 00:48:31,030 --> 00:48:35,290 The reed-clogged waters of a river delta are full of potential riches, 372 00:48:35,450 --> 00:48:38,330 not only for birds but for human beings. 373 00:48:38,830 --> 00:48:43,590 The reeds themselves are used for many purposes, but it's not an easy life here. 374 00:48:44,130 --> 00:48:46,920 Firm land on which to live is hard to find. 375 00:48:47,300 --> 00:48:52,640 In the Danube delta, the few solid sandbanks are tightly packed with dwellings. 376 00:48:52,970 --> 00:48:59,060 Earth has to be conserved with piles to prevent a slight change in the current washing it away. 377 00:48:59,640 --> 00:49:05,650 And there's the threat of a rise in the water level caused not only by rainstorms upstream 378 00:49:05,860 --> 00:49:10,650 but an unusually high tide, backed by a storm sweeping up from the sea, 379 00:49:10,820 --> 00:49:13,320 which can cause devastating floods. 380 00:49:15,910 --> 00:49:19,870 In the twin joined deltas of the Tigris and Euphrates in Iraq, 381 00:49:20,080 --> 00:49:24,670 the marsh Arabs have become specialists in an amphibian life. 382 00:49:32,470 --> 00:49:35,890 Their houses seem to have solid enough foundations. 383 00:49:36,310 --> 00:49:40,560 In fact, they are floating on rafts of reeds. 384 00:49:57,700 --> 00:50:00,410 Some are the most elaborate constructions, 385 00:50:00,620 --> 00:50:07,040 yet all these soaring arches and roofs are also made from bundles of reeds. 386 00:50:07,670 --> 00:50:14,800 And reeds provide food for the livestock, so gathering them is a daily and never-ending chore. 387 00:50:30,360 --> 00:50:35,780 The herds have to be as much at home in the water are they are on their floating platforms 388 00:50:45,750 --> 00:50:48,880 The rewards of this precarious existence are, of course, 389 00:50:49,090 --> 00:50:53,840 the abundant fish which live all around the houses and even underneath them. 390 00:50:57,930 --> 00:51:03,730 So the fish and the marsh Arabs and the pelicans all flourish in one integrated community. 391 00:51:03,930 --> 00:51:08,150 The river has delivered the minerals it eroded from the mountains 392 00:51:08,310 --> 00:51:11,480 and the nutrients it collected from the forests. 393 00:51:12,070 --> 00:51:16,950 They sustain plants which are the food for small animals which are eaten by fish 394 00:51:17,110 --> 00:51:20,700 and which are gathered by great flocks of birds 395 00:51:20,910 --> 00:51:25,500 that, from the tropics to the Arctic, are the glories of the deltas. 396 00:51:32,250 --> 00:51:35,760 A blizzard of snow geese in northern Canada. 397 00:51:42,310 --> 00:51:47,850 Across the world in the tropics, on a delta in Papua New Guinea, magpie geese. 398 00:51:56,360 --> 00:51:59,700 In Australia, brolga cranes. 399 00:52:07,870 --> 00:52:10,830 Scarlet ibis in Venezuela. 400 00:52:13,130 --> 00:52:19,010 Plovers on almost any delta in the world. And, equally widespread, stilts. 401 00:52:35,480 --> 00:52:37,950 Flamingos in Africa. 402 00:52:47,750 --> 00:52:49,410 And spoonbills. 403 00:52:56,960 --> 00:53:01,970 Of all the deltas in the world, none is greater than that of the Amazon. 404 00:53:10,850 --> 00:53:13,310 For hundreds of miles along its lower course, 405 00:53:13,520 --> 00:53:18,860 the river has been so broad that it has been impossible to see from one side to another. 406 00:53:19,360 --> 00:53:24,870 Now, instead of receiving more tributaries, it splits into a tangle of separate channels. 407 00:53:27,830 --> 00:53:33,540 And on the last firm land on its banks stands a great and thriving port, 408 00:53:34,040 --> 00:53:37,960 for the river is so wide and deep that cargo ships from overseas 409 00:53:38,130 --> 00:53:44,850 can use it as a highway that can take them for 1,000 miles into the heart of South America. 410 00:53:46,810 --> 00:53:50,310 The Amazon's vital statistics are astounding. 411 00:53:50,600 --> 00:53:56,860 At any one time, two thirds of all the river water in the world is flowing between its banks. 412 00:53:57,190 --> 00:54:03,490 Here at its mouth, at Belem, it's 200 miles across a maze of channels and islands, 413 00:54:03,780 --> 00:54:07,780 one of which is, alone, bigger than the whole of Switzerland. 414 00:54:07,950 --> 00:54:14,540 The river maintains its identity far into the sea. It was because of this that it was discovered. 415 00:54:14,710 --> 00:54:19,880 In 1499 a Spanish sea captain, sailing well beyond the sight of land, 416 00:54:20,050 --> 00:54:25,390 suddenly became aware that the water he was crossing was fresh and not salty. 417 00:54:25,640 --> 00:54:29,310 He turned west and discovered this immense river. 418 00:54:29,560 --> 00:54:34,270 Indeed, it's not until 100 miles beyond the edge of the continent 419 00:54:34,440 --> 00:54:40,900 that particles of water which fell on the Andes complete their 4,000-mile-long journey 420 00:54:41,110 --> 00:54:44,700 and mingle with the salt water of the ocean. 421 00:54:49,950 --> 00:54:56,170 But along the coast, where the thrust of the river flood is not so great, is a halfway house. 422 00:54:56,670 --> 00:55:00,670 Here the water is neither fresh nor salt, but brackish. 423 00:55:00,920 --> 00:55:04,420 It's neither land nor sea, but banks of mud and sand 424 00:55:04,630 --> 00:55:08,430 that are half the time submerged and half the time exposed.