0nly 3% of the water on our planet is fresh.|地球上只有3%的水是淡水

Yet these precious waters are rich with surprise.|可是这些珍贵的淡水中却充满了惊奇

All life on land is ultimately dependant upon fresh water.|所有陆地生命归根结底都依赖于淡水

行星地球3----淡水

The mysterious tepuis of Venezuela,|神秘的委内瑞拉平顶山区

isolated mountain plateaus rising high above the jungle.|一个孤立于丛林之上的的山地高原

This was the inspiration for Arthur Conan Doyle's Lost World,|这里是亚瑟·柯南·道尔的著作 《失落的世界》的灵感源泉

an imagined prehistoric land.|一个想象中的史前世界

Here, strange towers of sandstone have been sculptured over the millennia|这里伫立着数千年来暴风骤雨

by battering wind and torrential rain.|雕凿成的奇形怪状的石塔

Moisture, rising as water vapour from the surface of the sea,|水蒸发成水蒸气从海面升起

is blown inland by wind.|接着被风带到内陆

0n reaching mountains, the moist air is forced upwards|途经山脉的时候，水气被迫抬升

and as it cools, it condenses into cloud|逐渐冷却，汇聚成云

and finally rain, the source of all fresh water.|最后形成降雨，这便是所有淡水的来源

There is a tropical downpour here almost every day of the year.|这里全年几乎每天都会降下热带暴雨

Fresh water's journey starts here, high in the mountains.|淡水之旅就是从这些高山之巅开始的

Growing from humble streams to mighty rivers,|涓涓细流汇集成泱泱大河

it will travel hundreds of miles to the sea.|行程数百英里回到大海

Angel Falls, the highest waterfall in the world.|安赫尔瀑布——世界上落差最大的瀑布

Its waters drop unbroken for almost 1 ,000 metres.|流水不间断地从将近1000米的高处落下

Such is the height of these falls,|具有如此这般高度的瀑布

that long before the water reaches the base in the Devil's Canyon,|在水还未落到恶魔谷底之前

it's blown away as a fine mist.|便已被吹散成雾霾

In their upper reaches, mountain streams are full of energy.|上游地段的山涧充满活力

Streams join to form rivers|溪流汇聚成河

building in power|随着力道的积聚

creating rapids.|形成激流

The water here is cold|这里的水较冷

low in nutrients but high in oxygen.|营养物质不多，但含氧量却很高

The few creatures that live in the torrent|生活在急流中的少数几种动物

have to hang on for dear life.|得有办法固定自己以保住性命

Invertebrates dominate these upper reaches.|无脊椎动物统治着上游河段

The hellgrammite, its body flattened to reduce drag,|这是鱼蛉，其扁平的身体 能减少水的冲击力

has bushy gills to extract oxygen from the current.|并依靠浓密的鳃从水中过滤氧气

Black fly larvae anchor themselves with a ring of hooks.|蚋的幼虫靠钩环固定自己

But if these become unstuck|即使不小心松脱了

they're still held by a silken safety line.|它们还有一根坚韧的“安全索”

There are advantages to life in the fast stream.|这些动物拥有在急流中生存的先天优势

Bamboo shrimps can just sit and sift out passing particles|拟匙指虾只需趴在河底，用它们的扇形前臂从流水中

with their fan-like forearms.|过滤出食物颗粒

Usually these mountain streams only provide enough food|通常，山涧提供的食物

for small animals to survive|只能维持小型动物生存

but with the spring melt here in japan|可是在日本，每当春雪消融之际

monsters stir in their dens.|一种怪物便在巢窟中苏醒

Giant salamanders, the world's largest amphibian,|大鲵——世界上最大的两栖动物

almost two metres long.|几乎能长到2米长

They're the only large predator in these icy waters.|它们是这些冰水中唯一的大型掠食动物

They begin their hunt at night.|夜幕降临，它们开始捕猎

These salamanders have an exceptionally slow metabolism.|大鲵的新陈代谢十分缓慢

Living up to 80 years, they grow into giants.|它们能活80多年，因此长得十分巨大

The fish they hunt are scarce|可供大鲵捕食的鱼非常稀少

and salamanders have poor eyesight.|而且它们的视力也很差

But sensory nodes on their head and body|可是它们头上和身上的感官突起

detect the slightest changes in water pressure.|能觉察出最轻微的水压变化

Free from competition|由于没有竞争

these giants can dine alone.|这些大家伙得以独自享用美食

Pickings are usually thin for the salamanders,|大鲵的收获通常都比较少

but every year some of the world's high rivers are crowded by millions of visitors.|而世界上的高山河流每年都将 迎接成千上万的来访者

The salmon have arrived.|鲑鱼来了

This is the world's largest freshwater fish migration.|这是世界上规模最大的淡水鱼洄游

Across the northern hemisphere|鲑鱼穿越整个北半球

salmon, returning from the ocean to their spawning grounds,|从海洋回到它们的产卵地

battle their way for hundreds of miles upstream.|奋力逆流而上数百英里

Up here there are fewer predators to eat their eggs and fry.|只因上游很少有捕食鱼卵 和鱼苗的掠食者

A grizzly bear.|一只灰熊

From famine to feast|它已经很久没有打牙祭了

he's spoilt for choice|早就盼着这个机会

This Canadian bear is very special.|这只加拿大熊很特别

He's learnt to dive for his dinner.|它学会了潜水捕猎

But catching salmon in deep water is not that easy,|但要想在深水中捕获鲑鱼可不太容易

and the cubs have lots to learn.|熊崽们还要很多东西要学

The annual arrival of spawning salmon brings huge quantities of food|鲑鱼每年都会到河里产卵，同时也为其他动物提供了美味大餐

into these high rivers that normally struggle to support much life.|而其他那些上游动物，平常只能勉强维生计

Although relatively lifeless|尽管高山河流的生物量相对较少

the power of these upland rivers to shape the landscape|它们却有能力改变地形

is greater than any other stage in a river's life.|在河流扮演的角色中，这才是最主要的

Driven by gravity, they're the most erosive forces on the planet.|它们借助地心引力，成为地球上最大的侵蚀力量

For the past five million years,|在过去的500万年中

Arizona's Colorado River has eaten away at the desert sandstone|亚利桑那州的科罗拉多河 冲走了大量沙石

to create a gigantic canyon.|形成一个巨大深邃的峡谷

It's over a mile deep|它的深度超过1英里

and at its widest, it's 1 7 miles across.|最宽的地方达17英里

The Grand Canyon.|这就是大峡谷

This river has cut the world's longest canyon system,|这条河冲蚀出了世界上最长的峡谷系

a 1 ,000 mile scar clearly visible from space.|在太空中也能清楚地看到 这条长达1000英里的沟壑

As rivers leave the mountains behind,|河流离开山区之后

they gradually warm and begin to support more life.|河水渐渐变暖，养育的动物也多了起来

Indian rivers are home to the world's most social otter.|印度河里住着世界上最具社会性的水獭

Smooth-coated otters form family groups up to 1 7 strong.|印度水獭的一个家族可多达17名成员

Group rubbing not only refreshes their coats,|集体“按摩”不仅能清洁它们的皮毛

but strengthens social bonds.|也能增强群体内部团结

When it comes to fishing|当它们去捕鱼时

there is real strength in numbers.|群体合作能保证它们屡战屡胜

Fishing practice begins when the cubs are four months old.|小水獭在4个月大时就开始学习捕鱼

0nly the adults have the speed and agility needed to make a catch.|只有成年水獭才具备 捕鱼所需的速度和灵巧

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Adults share their catches with their squabbling cubs.|成年水獭把“战利品”与幼崽一起分享，小家伙们立刻抢成一团

Most otters are solitary,|大部分水獭都是独自生活

but these rich, warm waters can support large family groups|但是这些富饶温暖的水域 足以养活大型家族

and even bigger predators.|甚至更大的掠食动物

Mugger crocodiles, four metres long, could easily take a single otter.|4米长的恒河鳄 能轻松捕获一只落单的水獭

But confident in their gangs,|不过集合起来的水獭颇有胆量

the otters will actively harass these great reptiles.|反而会主动骚扰这些大块头的爬行动物

Team play wins the day.|群体作战通常会取得胜利

The Mara River, snaking across the plains of East Africa.|马拉河蜿蜒地穿过东非平原

As the land flattens out|由于地势平坦

rivers slow down and lose their destructive power.|河水流速变慢，没有了原来的破坏力

Now they're carrying heavy loads of sediment|河流中带着大量的泥沙

that stains their waters brown.|水变得很浑浊

Lines of wildebeest are on the march.|一队队的角马正在迁徙途中

Each year, nearly two million animals migrate|每年都会有将近200万只角马

across the Serengeti Plains|横越塞伦盖蒂平原

in search of fresh, green pastures.|去寻找新鲜草场

For these thirsty herds,|对于这群饥渴难耐的角马来说

the rivers are not only a vital source of drinking water|河流不仅是唯一能解渴的重要水源

but also dangerous obstacles.|也是充满危险的关隘

This is one of the largest concentrations of Nile crocodiles in Africa,|这里是非洲一处最大的尼罗鳄聚集地

giants that grow over five metres long.|这些大怪物能长到5米多长

From memory, the crocodiles know the wildebeest are coming|鳄鱼凭着记忆得知，角马已经来了

and gather in anticipation.|不出所料，它们纷纷下水

The crocodile's jaws snap tight like a steel trap.|鳄鱼的巨口像捕兽铗一般紧咬住猎物

0nce they have a hold, they never let go.|一旦被它逮住，猎物再无逃脱的机会

It took over an hour to drown this full-grown bull.|它得花上一个多小时 才能淹死这只成年公角马

To surprise their prey|为了突袭猎物

crocodiles must strike with lightning speed.|鳄鱼必须以闪电般的速度出击

Here, only the narrowest line separates life from death.|在这里，生与死只有一线之隔

Most rivers drain into the sea,|大部分河流都汇入大海

but some end their journey in vast lakes.|可有些河流的终点却是大型湖泊

Worldwide, lakes hold 20 times more fresh water than all the rivers.|全球湖泊淡水储量比江河多20倍

The East African Rift Valley holds three of the world's largest,|东非大裂谷内有着3个世界上最大的淡水湖

Malawi, Tanganyika and Victoria.|马拉维湖、坦噶尼喀湖，以及维多利亚湖

Lake Malawi, the smallest of the three|马拉维湖是这3个湖泊中最小的

is still bigger than Wales.|却仍比威尔士还要大

Its tropical waters teem with more fish species than any other lake.|生活在这个热带湖泊里的鱼类 比其它湖泊都要丰富

There are 850 different cichlids alone,|这里有850多种不同的慈鲷

all of which evolved from just one single ancestor|它们都是从一个数千年前

isolated here thousands of years ago.|即被隔绝在此的祖先进化而来的

These two-metre wide craters are fish-made.|这些2米宽的土丘是鱼儿们的杰作

Fastidiously maintained by the males, these bowers are courtship arenas.|雄鱼一丝不苟地维护着坑巢，因为这里正是求爱的场所

Cichlids are caring parents.|慈鲷是尽心尽职的父母

Brooding young in the mouth is a very effective way of protecting them.|它们将鱼苗含在嘴里，这是一种保护它们的有效方法

This lake can be a dangerous place.|马拉维湖也是个危机四伏的地方

After dark, predatory dolphin fish emerge from their daytime lairs among the rocks.|到了晚上，掠食性的长颌鱼纷纷 游出它们白天潜伏的石缝

Like packs of sharks, they're on the prowl for sleeping cichlids.|它们像是一群鲨鱼，一边游一边寻找熟睡中的慈鲷

In the darkness, these electric fish hunt by detecting distortions|黑暗中，这些鱼捕猎依靠感知

in the electric field they create around their bodies.|它们在身体周围形成电场的变化

(CRACKLING)

Any cichlid that ventures out will be snapped up.|一旦慈鲷切入电场，立刻就会成为捕食的对象

The floor of Lake Malawi drops 700 metres into an abyss.|马拉维湖底是一个深达700多米的深渊

Here in this dead zone|这个死亡地带成了

the larvae of lake fly midges hide out away from predators.|幽蚊幼虫躲避天敌的庇护所

In the rainy season, they balloon up to the surface|每到雨季，它们便充气浮上水面

and undergo a magical transformation.|然后经历一场不可思议的变化

At dawn, the first adult midges start to break out.|黎明时分，第一只成蚊破蛹而出

Soon, millions upon millions of newly-hatched lake flies|不久，成百上千万只新羽化的幽蚊

are taking to the wing.|全都扇动着翅膀飞到空中

Early explorers told tales of lakes that smoked as if on fire.|早期探险家看到这种湖面上“冒烟”的情景，还以为是湖底着了火

But these spiralling columns, hundreds of metres high,|这些高达数百米的螺旋型“烟”柱

are mating flies.|其实是正在交配的幽蚊

0nce the flies have mated|幽蚊完成交配之后

they will all drop to the water surface,|便会一起落到水面

release their eggs and die.|产下卵，然后死去

Malawi may look like an inland sea,|马拉维湖看起来像大海一样辽阔

but it's dwarfed by the world's largest lake.|但它远比不上世界上最大的湖泊

Baikal in eastern Siberia.|东西伯利亚的贝加尔湖

Four hundred miles long and over a mile deep,|贝加尔湖长400英里，深度超过1英里

Baikal contains one-fifth of all the fresh water found in our planet's lakes and rivers.|其中的淡水储量占到了全球江河湖泊淡水总量的1/5

For five months of the year, it's sealed by an ice sheet over a metre thick.|每年中总有5个月，湖面被1米厚的冰层覆盖

Baikal is the oldest lake in the world|贝加尔湖是世界上最古老的湖泊

and despite the harsh conditions, life flourishes here in isolation.|尽管生存条件恶劣，生命仍在这个与世隔绝的地方得到了兴盛

80% of its species are found nowhere else on Earth,|湖里80%的物种 在地球上其它地方都不存在

including the world's only freshwater seal.|包括世界上唯一的淡水海豹

With this seal|有了这种海豹

and its marine-like forests of sponges|再加上海底森林一般的海绵

Baikal seems more like an ocean than a lake.|贝加尔湖看起来 更像是海洋，而不是湖泊

There are shrimp-like crustaceans, giant amphipods as large as mice.|这种长得像虾一样的甲壳动物 是一种大型端足类动物，它有老鼠那么大

They are the key scavengers in this lake.|它们是湖里不可或缺的“清洁工”

The water here is just too cold for the bacteria that normally decompose the dead.|由于湖水过于寒冷，分解尸体的细菌很难在此存活

Most rivers do not end in lakes|大部分河流并非止于湖泊

but continue their journey to the sea.|而是一直奔向大海

The planet's indisputable super river is the Amazon.|地球上的超级大河 毫无疑问就是亚马逊河

It carries as much water as the next top 1 0 biggest rivers combined.|它的水量是世界十大江河中 其余9条大河的总和

Rising in the Peruvian Andes, its main trunk flows eastwards across Brazil.|它发源于秘鲁安第斯山区，其干流穿越整个巴西

0n its way, the system drains a third of South America.|全部流域面积达到南美洲的1/3

Eventually, over 4,000 miles from its source|最终，在经过4000英里的流程之后

it empties into the Atlantic 0cean.|亚马逊河汇入了大西洋

The Amazon transports a billion tonnes of sediment a year,|亚马逊河每年会带来10亿吨的泥沙

sediment clearly visible at the mixing of the waters,|泥沙使得河水交汇成为一道显眼的风景

where one massive tributary, the Rio Negro, flows into the main river.|一条巨大的支流 ——内格罗河在此汇入干流

Its waters are wonderfully rich.|河水中的物种异常丰富

To date, over 3,000 species of their fish have been described,|据统计，被命名的鱼类已达到3000多种

more than in the whole of the Atlantic 0cean.|这比整个大西洋的鱼类种数还要多

The Amazon is so large and rich in fish|亚马逊河养育着丰富繁多的鱼类

that it can support freshwater dolphins.|为淡水海豚提供了生存条件

These botos are huge, 2.5 metres long.|这些亚马逊江豚体型巨大，身长达2.5米

In these murky waters, they rely on sonar to navigate and hunt.|它们利用回声定位 在昏暗的水中探路和捕食

They work together to drive shoals of fish into the shallows.|它们一起合作把鱼群赶到浅水区

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Botos are highly social|亚马逊江豚是高度社会型动物

and in the breeding season, there is stiff competition for mates.|在繁殖季节，会有一场激烈的求偶竞赛

The males hold court in a unique way.|雄江豚会以独特的方式向雌江豚示爱

They pick up rocks in their jaws|它们用长嘴捡起石块

and flaunt them to their attending females.|然后向自己的“心上人”炫耀

Maybe each male is trying to show how strong and dexterous he is|这或许是雄江豚展示自己 强壮身体和敏捷身手的一种方式

and that he therefore is the best father a female could have for her young.|以此来证明自己将是最好的父亲，雌江豚为了孩子就应该选它

Successful displays lead to mating.|求爱成功后，它们便开始交配

Even for giant rivers like the Amazon,|即使像亚马逊河这般巨大的江河

the journey to the sea is not always smooth or uninterrupted.|流向大海的过程也并非都是平缓连续的

Iguagu Falls, on the border of Brazil and Argentina,|位于巴西和阿根廷边境的伊瓜苏瀑布

is one of the widest waterfalls in the world|是世界上最宽的瀑布之一

1.5 miles across.|宽幅达1.5英里

In flood, 1 3 million litres of water spill over every second.|瀑布每秒的水流量达到3000万立方米

All the world's great broad waterfalls,|所有世界上最大的瀑布

Victoria, Niagara and here, Iguagu,|维多利亚瀑布、尼亚加拉瀑布，还有这里的依瓜苏瀑布

are only found in the lower courses of their rivers.|都是位于河流的下游地段

In their final stages,|在旅途的最后阶段

rivers broaden and flow wearily across their flat flood plains.|河道变宽，河水缓缓流过 平坦辽阔的冲积平原

Each wet season here in Brazil,|这里是巴西，每到雨季

the Parana river overflows its banks|巴拉那河都会泛滥

and floods an area the size of England.|洪水淹没的地区相当于一个英格兰

The Pantanal|潘塔纳尔沼泽地

the world's largest wetland.|世界上最大的湿地

In these slow-flowing waters, aquatic plants flourish,|缓慢的流水中生长着茂盛的水生植物

like the Victoria Giant Water Lily, with leaves two-metres across.|譬如有着2米宽叶子的王莲

These underwater forests are nursery grounds for fish.|这些水下森林正是 鱼类理想的“育婴”场所

0ver 300 species breed here, including red-bellied piranha.|大约有300多种动物在此繁殖，其中包括红腹锯脂鲤

And other predators, like the spectacled caiman.|以及其它食肉动物，例如眼镜凯门鳄

Ripening fig trees, overhanging the water's edge|水边生长着高大的无花果树

provide welcome food for shoals of hungry fish.|为饥饿的鱼群提供美味食物

The commotion attracts dorado|骚动引来了麻哈脂鲤

known locally as the river tiger.|当地人称之为“河中之虎”

They patrol the feeding shoals|它们穿梭于觅食的鱼群中

looking for a chance to strike.|找准机会发动进攻

And waiting in the wings|有些鱼则守在一旁等待

ready to pick off any injured fish,|时刻准备攻击任何受伤的鱼

are the piranhas.|它们就是锯脂鲤

A feeding frenzy quickly develops.|它们的进食速率极快

Piranha can strip a fish to the bone in minutes.|锯脂鲤几分钟内便能 将一条活鱼啃得只剩下骨架

Great numbers of fish sustain vast flocks of water birds.|大量的鱼养活着大批聚集的水鸟

The roseate spoonbill is just one of the 650 bird species|粉红琵鹭是潘塔纳尔沼泽地中的

found in the Pantanal.|650多种鸟类中的一种

They nest alongside woodstorks in colonies thousands strong.|它们将巢建在树干上，一群多达好几千只

Spectacled caiman linger below|眼镜凯门鳄在下面游荡

waiting for a meal to fall out of the sky.|等着食物从天而降

When rivers finally reach the sea,|当江河最终汇入大海时

they slow down, release their sediment and build deltas.|水流减缓，留下大量泥沙，堆成了三角洲

In Bangladesh, the Ganges and Brahmaputra rivers|在孟加拉国，恒河与雅鲁藏布江的交汇处

join to form the world's biggest.|形成了世界上最大的三角洲

Every year, almost 2,000 million tonnes of sediment|每年大约有20亿吨泥沙在此沉淀

eroded from the Himalayas|从喜马拉雅山脉上 崩塌下来的土石

is delivered to the ocean.|最终归于大海

At the delta's mouth, the largest mangrove forest in the world,|三角洲河口地带有一片 世界上最大的红树林

the Sunderbans.|孙德尔本斯红树林

These extraordinary forests spring up throughout the tropics|这些特殊的树林遍及整个热带地区的潮间带

in these tidal zones where rivers meet the sea.|那里正是河流的入海口

Crab-eating macaques are mangrove specialists.|食蟹猴是红树林的特有物种

In Indonesia, these monkeys have adopted a unique amphibious lifestyle.|在印度尼西亚，这些猴子 过着一种独特的双栖式生活

They fish out fallen food.|它们拣食落在水中的食物

The troop also uses the waters to cool off during the heat of the day.|在白天酷热难耐之时，猴群会利用水来给身体降温

But the channels are also the playground for restless young macaques.|水道也是顽皮的小猴子们的游乐场

Some of the young have even taken to underwater swimming.|有的小猴甚至已经学会潜泳

They can stay down for more than 30 seconds|它们能在水下呆30多秒

and appear to do this just for fun.|而它们这么做似乎只是因为好玩

Yet these swimming skills acquired during play|但是，这些在玩耍中学会的游泳本领

will certainly be useful later in life in these flooded mangrove forests.|将来会成为在红树林中 非常有用的生活技能

In cooler climes, mud laid down in estuaries|在较冷的地区，沉积在入海口的泥沙

is colonised by salt marsh grasses|被大片盐沼水草覆盖

and form one of the most productive habitats on the planet.|成为地球上一处 最肥沃的野生动物栖息地

Four hundred thousand greater snow geese flock to the estuaries|40万只大西洋雪雁成群飞往

along the Atlantic coast of the United States|美国大西洋海岸的河口地带

to rest and refuel on their long migratory journeys.|并在此休整，准备继续长途迁徙

This is the end of the rivers' journey.|这是淡水之旅的终点

Collectively, they've worn down mountains|它们共同抚平高山

and carried them to the sea.|把它们带向大海

And all along the way,|在整个行程中

their fresh water has brought life in abundance to planet Earth.|淡水为地球带来了无数生机与富饶