0:00:35 > 0:00:38Do you know what?
0:00:38 > 0:00:40I think it's going to rain.
0:00:45 > 0:00:48Water.
0:00:48 > 0:00:53Can you imagine anything more pure, more elemental?
0:00:54 > 0:00:59There's not a plant or animal on earth that can do without it.
0:01:00 > 0:01:06And when it falls as rain, it brings the entire British Isles to life.
0:01:12 > 0:01:17Like water off a duck's back, it drips from the leaves.
0:01:17 > 0:01:20The drips become trickles,
0:01:20 > 0:01:23trickles become streams.
0:01:23 > 0:01:27And before you know it, a roaring river is born.
0:01:35 > 0:01:38Water seems such simple stuff,
0:01:38 > 0:01:44yet when it interacts with the land, it creates such extraordinary variety.
0:01:44 > 0:01:52Rushing streams and lazy rivers, reed beds and bogs, lakes and canals.
0:01:52 > 0:01:56The only thing they have in common is that water runs through them.
0:02:02 > 0:02:07But how can something so pure and simple create so many opportunities
0:02:07 > 0:02:13for wildlife, and produce such a diversity of habitats?
0:02:13 > 0:02:21Come with me on a journey from the source to the sea, as we discover Freshwater Britain.
0:02:29 > 0:02:32What better place to start than Scotland?
0:02:32 > 0:02:35So wet, they had to invent the Macintosh.
0:02:35 > 0:02:39They say if you can see the hills, it's about to rain.
0:02:39 > 0:02:41And if you can't,
0:02:41 > 0:02:43it's raining.
0:02:45 > 0:02:48The uplands are where most of our rivers start.
0:02:48 > 0:02:52And with their heavy rains, comes drama.
0:02:54 > 0:02:58The first thing that strikes you is the water's incredible power.
0:02:58 > 0:03:02Tonnes of it come cascading over these rocks every second.
0:03:02 > 0:03:04I've got to shout just to make myself heard.
0:03:04 > 0:03:08CASCADING WATER THUNDERS
0:03:08 > 0:03:12Now, you and I might be tempted to go with the flow.
0:03:12 > 0:03:16But there's one creature that fights it all the way.
0:03:18 > 0:03:20The Atlantic salmon.
0:03:20 > 0:03:23It's such a Herculean effort.
0:03:23 > 0:03:28Even though they were born to swim and born to do this, it must take so much energy out of them.
0:03:31 > 0:03:38They started life in this very river, but at just a few months old were swept out to sea.
0:03:40 > 0:03:46They spent up to four years in the open ocean, building up the strength to return.
0:03:48 > 0:03:53But to make it, they need every ounce of energy they possess.
0:04:00 > 0:04:04Only upstream will the salmon find a mate, and to get there
0:04:04 > 0:04:08it must battle against the flow every step of the way.
0:04:25 > 0:04:31Beyond these falls, nestled in the Highlands, is the river where they started life.
0:04:33 > 0:04:37They're drawn back by its memory.
0:04:37 > 0:04:41After four years, they can still remember the taste.
0:04:42 > 0:04:47As their energy ebbs, it's that memory that drives them on.
0:04:50 > 0:04:58They won't eat or rest until they've reached their birthplace, or died trying.
0:05:12 > 0:05:16As the salmon risk their lives battling this torrent of water,
0:05:16 > 0:05:21they pass another creature that actually takes advantage of the flow.
0:05:33 > 0:05:36DIPPERS SING
0:05:39 > 0:05:41This is a dipper.
0:05:42 > 0:05:45It's related to the robins and wrens in your garden.
0:05:47 > 0:05:49But would they do this?
0:05:53 > 0:05:57The dipper is the only British songbird to hunt underwater.
0:05:57 > 0:06:01It's even known to swallow stones to help it sink.
0:06:01 > 0:06:06And the thing that makes life tough for a salmon keeps the dipper alive.
0:06:10 > 0:06:15They say that still waters run deep, but the opposite's also true.
0:06:15 > 0:06:20Fast-flowing water, on steep slopes, runs shallow.
0:06:20 > 0:06:22And that's why you only find dippers here.
0:06:22 > 0:06:26The water's shallow enough to dive down for their dinner.
0:06:39 > 0:06:42DIPPERS SING
0:06:46 > 0:06:52But water doesn't just flow over the landscape - it creates landscapes.
0:06:52 > 0:06:57The riffles, pools and waterfalls that make up the dipper's home
0:06:57 > 0:07:01have been carved out by the water's erosive power.
0:07:01 > 0:07:06It's this power that makes the salmon's journey so difficult.
0:07:06 > 0:07:12But it's also the very reason that it has to make the journey.
0:07:12 > 0:07:16It's only here, in the very place where they were born,
0:07:16 > 0:07:20that the water's fast enough to scour the gravel clean of silt.
0:07:20 > 0:07:26Without fast water, the eggs they've come all this way to lay, would simply be buried alive.
0:07:31 > 0:07:36The ones that made it now assume their breeding colours, a rich red.
0:07:36 > 0:07:41And for the males, hooked jaws, because the battle is no longer
0:07:41 > 0:07:44against the flow, but with each other.
0:07:47 > 0:07:54On arrival, the females turn their tails from the task of swimming, to digging a nest.
0:07:59 > 0:08:02The effort can leave them in tatters.
0:08:05 > 0:08:09The males, meanwhile, fend off the local competition,
0:08:11 > 0:08:16although having worked so hard to get here, rivals can prove rather persistent.
0:08:31 > 0:08:38Once they've seen off all comers, they set to wooing their mate with a shivering caress.
0:08:38 > 0:08:41But fighting the flow has hit them hard.
0:08:41 > 0:08:49The fast water will keep their eggs alive, but battling it all the way has left them exhausted.
0:08:49 > 0:08:54For almost every one of them, this is the last journey they'll ever make.
0:09:00 > 0:09:05As the year ends, their bodies litter the banks.
0:09:05 > 0:09:11And these fallen fish make a meal fit for the king of birds.
0:09:16 > 0:09:22On the Isle of Mull, sea eagles feast on the dead and the dying.
0:09:52 > 0:09:58But beneath the fast-flowing water, the salmon have left their legacy.
0:10:00 > 0:10:06A legacy forged through raging rivers and towering falls.
0:10:09 > 0:10:15Buried beneath the gravel are hundreds of thousands of developing eggs.
0:10:15 > 0:10:22Next spring they'll hatch, and before long, they too will be swept out to sea.
0:10:22 > 0:10:25Most will never make it.
0:10:25 > 0:10:31But crucially, a handful will survive to return.
0:10:38 > 0:10:42But it's not just wildlife that's affected by fast-flowing water.
0:10:42 > 0:10:45Its erosive powers have created some of
0:10:45 > 0:10:50Britain's most memorable scenery, like here in the Yorkshire Dales.
0:10:50 > 0:10:53Water is powerful stuff.
0:10:53 > 0:10:56Every cubic metre weighs a tonne.
0:10:56 > 0:11:03So it's no surprise that it's had a greater impact in shaping our landscape than anything else.
0:11:03 > 0:11:09Especially here, in a place close to my heart, the north of England.
0:11:11 > 0:11:15If you did geography at school, chances are
0:11:15 > 0:11:19you've studied this place - Malham in the Yorkshire Dales.
0:11:19 > 0:11:25Nearby, Gordale Scar, carved out over millions of years by the Gordale Beck.
0:11:29 > 0:11:36And Malham Cove, looking for all the world like a waterfall without the water, which is exactly what it is.
0:11:37 > 0:11:42At the end of the last glaciation, meltwater plummeted over these cliffs.
0:11:44 > 0:11:51And during the last Ice Age, vast rivers of frozen freshwater - glaciers -
0:11:51 > 0:11:58bulldozed their way through Britain, giving us the deep U-shaped valleys of the dales,
0:11:58 > 0:12:01and the dramatic scenery of the Lake District.
0:12:05 > 0:12:10Across the border, in County Durham, the River Tees is responsible for
0:12:10 > 0:12:14creating one of the highest waterfalls in England.
0:12:16 > 0:12:19The mighty High Force.
0:12:22 > 0:12:29All over Britain, freshwater has created some of our most dramatic and beautiful landscapes.
0:12:29 > 0:12:34And everywhere it flows it brings life to our British Isles.
0:12:44 > 0:12:48But it's not all drama on a huge scale.
0:12:48 > 0:12:52Spare a thought for the smaller creatures living up here.
0:12:53 > 0:13:00I mean, life's no picnic for them either in fast running water, which is what I'm here to show you.
0:13:00 > 0:13:06Now then, the place to look for them is underneath these rocks.
0:13:06 > 0:13:09Oh, look at that. Caddis fly larvae.
0:13:09 > 0:13:12They surround themselves with these lumps of stone,
0:13:12 > 0:13:16to protect them from the water and from predators. Oh and here...
0:13:16 > 0:13:20Oh, come on. Look at that.
0:13:20 > 0:13:23Flat as a pancake. I haven't squashed it. It's a mayfly larva.
0:13:23 > 0:13:27It's flat like that for a good reason so the water passes over it,
0:13:27 > 0:13:30rather like air flowing over a Formula 1 racing car.
0:13:30 > 0:13:35That's something that all the insects here share. They're clinging on for dear life.
0:13:38 > 0:13:43When it's underwater and not stuck to my finger, you can really see
0:13:43 > 0:13:46how perfectly shaped the mayfly larva is.
0:13:52 > 0:13:54And here's another caddis.
0:13:54 > 0:13:59This one builds a stone house to weigh it down, but lugs it around.
0:13:59 > 0:14:02Not easy, but better than being swept out to sea.
0:14:02 > 0:14:10So given the difficulties, what is it that makes fast-moving water so attractive to insects like these?
0:14:10 > 0:14:13Well, it's another insect, and one of our most beautiful
0:14:13 > 0:14:17freshwater creatures that can help us unravel the mystery.
0:14:22 > 0:14:26And to see that, we have to leave the turbulent waters of our uplands
0:14:26 > 0:14:31and journey south, to one of our gentler, lowland rivers.
0:14:31 > 0:14:37Only here can we see another advantage that fast flow brings.
0:14:37 > 0:14:41This is the River Thame in Buckinghamshire.
0:14:41 > 0:14:47And on lazy summer days, damselflies dance over the water's surface.
0:14:49 > 0:14:57These are banded demoiselles, and they love slow-moving rivers - except when it comes to mating.
0:14:57 > 0:15:01Then, it's the faster-flowing areas that everyone wants.
0:15:01 > 0:15:07And the males, in their shining metallic armour, are prepared to do battle over them.
0:15:39 > 0:15:44By landing, they lay claim to a small stretch of river.
0:15:44 > 0:15:48But that takes nerve in the face of an adversary's flashing wings.
0:16:04 > 0:16:09Crucially, they've captured an area of slightly faster-flowing water.
0:16:09 > 0:16:14It might only be the smallest riffle as the river races around a fallen branch.
0:16:14 > 0:16:18In fact, to you or me, it may not look much different.
0:16:18 > 0:16:26But believe me, to the female damselfly, this slightly faster water is incredibly important.
0:16:26 > 0:16:32And the males gamble everything to show the watching females just how fast it is.
0:16:35 > 0:16:43Risking attack from below, the males throw themselves on the water's surface and float downstream.
0:16:55 > 0:17:02Only if she's suitably impressed will the relationship be consummated in a cartwheel embrace.
0:17:03 > 0:17:08And the reason for her careful choice is finally revealed.
0:17:10 > 0:17:18In this tiny patch of fast-flowing water, the female damsel struggles through the water's surface.
0:17:20 > 0:17:23And there, she lays her eggs.
0:17:25 > 0:17:29For only here, where the current runs swiftly,
0:17:29 > 0:17:33is there enough oxygen to give her young the best possible start.
0:17:37 > 0:17:42Imagine being locked in a room where all the doors and windows are sealed.
0:17:42 > 0:17:46It wouldn't be long before the air became stagnant and you started to suffer.
0:17:46 > 0:17:50But then imagine opening all those doors and windows,
0:17:50 > 0:17:54and allowing a cool, refreshing breeze to blow through.
0:17:54 > 0:17:56Well, that's what current brings -
0:17:56 > 0:18:01lots of crystal-clear water that's packed with oxygen.
0:18:03 > 0:18:07In the slower flow, insects like the diving beetle larva
0:18:07 > 0:18:11rely on snorkels so they can breathe from the surface.
0:18:11 > 0:18:16Or, like scuba divers, some insects take their air supply with them.
0:18:16 > 0:18:21The silvery sheen on this water boatman is an air bubble it carries with it.
0:18:23 > 0:18:28But the damselflies have chosen a different path.
0:18:28 > 0:18:33By risking the faster flow, their young can thrive in water
0:18:33 > 0:18:39rich with oxygen, which is just as vital to wildlife underwater, as it is for us above.
0:18:44 > 0:18:48To discover the next factor affecting our freshwater habitats,
0:18:48 > 0:18:53why don't you join me on the banks of another sun-drenched lowland river?
0:18:53 > 0:18:57Oh no, sorry - that was just drenched!
0:19:04 > 0:19:05Got your waders on? Come on then.
0:19:05 > 0:19:10What I'm hoping is that I can get you close to one of Britain's best-loved animals.
0:19:10 > 0:19:15It's one of the top predators on this river here, and there's one every few hundred yards.
0:19:15 > 0:19:19But what we need is a lot of patience, some peace and quiet
0:19:19 > 0:19:21and this branch.
0:19:25 > 0:19:27What I need to do now
0:19:27 > 0:19:35is tuck myself in here, make myself as invisible as possible, and then not move a muscle
0:19:35 > 0:19:38because if it sees me, it won't come anywhere near.
0:19:38 > 0:19:41Are you set?
0:19:41 > 0:19:43All we've got to do now is wait.
0:19:45 > 0:19:49It's just that nobody told me quite how long.
0:19:54 > 0:19:57Glamorous business, isn't it, this telly lark?
0:19:59 > 0:20:01But eventually, a familiar call.
0:20:01 > 0:20:03BIRD CHIRPS
0:20:03 > 0:20:06Can you hear? Can you hear that?
0:20:06 > 0:20:08That's it.
0:20:08 > 0:20:11It always sounds to me like a boatswain's whistle,
0:20:11 > 0:20:13piping somebody aboard.
0:20:14 > 0:20:16BIRD CHIRPS
0:20:18 > 0:20:20Got to keep absolutely still.
0:20:30 > 0:20:33It must be Britain's most brilliant bird.
0:20:35 > 0:20:37Even on a dull day it seems to shine.
0:20:47 > 0:20:49Suddenly the rain
0:20:49 > 0:20:51and the numb bum don't matter any more.
0:21:01 > 0:21:03It's an amazing sight.
0:21:03 > 0:21:09But the fact that these kingfishers are here, and in such large numbers on these lowland rivers,
0:21:09 > 0:21:14tells us something very important about this particular freshwater habitat.
0:21:23 > 0:21:29To support so many kingfishers, the water here must be packed full of fish.
0:21:29 > 0:21:32But why are there so many?
0:21:32 > 0:21:37To answer that I need to find the perfect place to do a spot of fishing.
0:21:37 > 0:21:42And where better than the Itchen, a chalk river in the heart of Hampshire.
0:21:56 > 0:22:03You've only got to look closely at a fly fisherman's tackle to realise the diversity of species out here.
0:22:04 > 0:22:06Perhaps I'd better rephrase that.
0:22:06 > 0:22:07Come and look at this.
0:22:09 > 0:22:16Sculpins and muddlers, zonkers and minkies.
0:22:16 > 0:22:18Aren't they wonderful names?
0:22:18 > 0:22:22And you've never seen so many different kinds of fishing fly.
0:22:22 > 0:22:26Here we have things like a daddy long legs, all hand tied.
0:22:26 > 0:22:32Here, larvae of different kinds of grubs and flies that might land on the water.
0:22:32 > 0:22:36And the reason there are so many of these is that there are so many
0:22:36 > 0:22:42insects on the river that the trout will take, and the fly fisherman has to do his best to emulate nature.
0:22:42 > 0:22:44But why are there so many of them?
0:22:44 > 0:22:48Why is this stream so rich in insect life?
0:22:48 > 0:22:52The answer is because it runs over chalk.
0:22:52 > 0:22:54It's all down to the rock.
0:23:01 > 0:23:07The figures decorating these hillsides owe their colour to the chalk rock below.
0:23:07 > 0:23:11But the rock does more than provide a palette for ancient artists.
0:23:14 > 0:23:21Chalk rivers start life as springs, emerging from deep within these hills.
0:23:21 > 0:23:24They're filtered crystal clear by the soft rock,
0:23:24 > 0:23:29which also breaks down in the water, adding minerals.
0:23:29 > 0:23:34These nourish a rich underwater garden, full of life.
0:23:41 > 0:23:46Wherever the rock is soft, water can easily pick up minerals.
0:23:46 > 0:23:49But chalk rivers are special.
0:23:49 > 0:23:57It's their unique qualities that make the region famous for its water meadows, like these in Salisbury,
0:23:57 > 0:24:00immortalised by the artist John Constable.
0:24:00 > 0:24:06Beautiful views for which, ultimately, we have the surrounding rock to thank.
0:24:09 > 0:24:16And if you want even further proof of how rich this habitat is, you need only take a peek
0:24:16 > 0:24:21beneath the watercress beds for which this region is famous.
0:24:23 > 0:24:31Lurking here in the quiet Hampshire countryside is one of Britain's most voracious predators.
0:24:31 > 0:24:35An animal with a deadly venomous bite.
0:24:35 > 0:24:39It's here because this is one of the few habitats in Britain
0:24:39 > 0:24:43productive enough to support its terrifying appetite.
0:24:43 > 0:24:44It's...
0:24:45 > 0:24:46..a shrew.
0:24:46 > 0:24:48A water shrew.
0:24:48 > 0:24:53Not a reason to stay indoors, but it does have a venomous bite.
0:24:53 > 0:24:57Harmless to us, but to its prey, quite deadly.
0:24:59 > 0:25:02Water shrews have no time to hang about.
0:25:02 > 0:25:05They're permanently ravenous -
0:25:05 > 0:25:09attacking sticklebacks, and even small frogs.
0:25:09 > 0:25:13Good job those venom-laden teeth aren't any bigger.
0:25:13 > 0:25:16And they're here because of their favourite food.
0:25:18 > 0:25:24Below the surface, like shoals of clockwork toys, swim tiny freshwater shrimp.
0:25:29 > 0:25:32Crucially, the water is packed full of nutrients
0:25:32 > 0:25:34dissolved from the soft rock.
0:25:34 > 0:25:37It's the chalk, crammed with calcium,
0:25:37 > 0:25:41that enables these tiny creatures to build their shells
0:25:41 > 0:25:43and exist in such numbers.
0:25:43 > 0:25:48Food enough to satisfy the most ravenous and rapid shrew.
0:25:50 > 0:25:52It's only by slowing them down
0:25:52 > 0:25:55that you can tell what on earth is going on.
0:25:59 > 0:26:02Shrews can smell under water.
0:26:02 > 0:26:04This is no mean feat for a mammal.
0:26:04 > 0:26:06Noses don't usually work down here.
0:26:06 > 0:26:10But by blowing tiny bubbles, and sucking the air back up that snout,
0:26:10 > 0:26:14they can sniff out the sweet smell of even the smallest shrimp.
0:26:17 > 0:26:21So without the soft rock, the plants wouldn't have the nutrients
0:26:21 > 0:26:23they need to grow lush and thick,
0:26:23 > 0:26:26nor the shrimp the calcium for their shells.
0:26:26 > 0:26:30And without them, the most voracious predator in Hampshire
0:26:30 > 0:26:33would soon run out of shrimp, and steam.
0:26:44 > 0:26:50But not all our rocks are as easily broken down as those soft southern ones.
0:26:50 > 0:26:53Let's leave Hampshire and travel back to Scotland,
0:26:53 > 0:26:58this time to visit the most famous bit of freshwater in Britain...
0:27:00 > 0:27:02..Loch Ness.
0:27:04 > 0:27:07Loch Ness is big, very big.
0:27:07 > 0:27:11It's so big that there's more water beneath my tiny boat
0:27:11 > 0:27:15than in all the rivers of England and Wales combined.
0:27:15 > 0:27:18It's enough to make you feel a bit vulnerable,
0:27:18 > 0:27:22especially when you consider what most people come here looking for.
0:27:26 > 0:27:30There's something mysterious beneath these dark waters.
0:27:34 > 0:27:39Something that reveals a great deal about this particular freshwater habitat.
0:27:52 > 0:27:54Oh, there you are.
0:27:54 > 0:27:57No, I've not come looking for Nessie,
0:27:57 > 0:28:02but there is a monster lurking down there in the depths of Loch Ness.
0:28:13 > 0:28:15And here it is.
0:28:21 > 0:28:23A ferox trout -
0:28:23 > 0:28:27ferox from the Latin, meaning "ferocious".
0:28:27 > 0:28:28And they are!
0:28:30 > 0:28:33They start life feeding on insects,
0:28:33 > 0:28:38but in Scottish lochs some of them turn, growing huge jaws
0:28:38 > 0:28:44and swelling to twice their normal size, becoming...well, monsters.
0:28:44 > 0:28:48They're the top predator in most Scottish lochs, and eating
0:28:48 > 0:28:53their fellow fish boosts their growth and lengthens their lives.
0:28:54 > 0:29:01Among fishermen, these ferocious ferox trout are almost as legendary as the great Nessie herself.
0:29:01 > 0:29:05But to find out what makes them the monsters they are, I need to look
0:29:05 > 0:29:10not down into the water, but back on the shore.
0:29:10 > 0:29:14It's these - the very rocks of Scotland themselves.
0:29:14 > 0:29:20Now, when water flows over soft rock, it picks up mineral nutrients that are vital for plant growth.
0:29:20 > 0:29:25But with rocks as hard as these, those nutrients remain locked up.
0:29:25 > 0:29:28So if the plants can't grow, insects can't feed on them,
0:29:28 > 0:29:33and the trout can't feed on the insects, so they turn into monsters.
0:29:33 > 0:29:39The ferox trout turn to eating their fellow fish because there aren't enough nutrients
0:29:39 > 0:29:46to support their normal prey, and this has big implications for the loch's more famous resident.
0:29:50 > 0:29:56Much as we'd like to believe that a prehistoric monster lurks beneath the waters of Loch Ness,
0:29:56 > 0:30:00the surrounding rocks mean that this sort of freshwater habitat
0:30:00 > 0:30:06is just too nutrient-poor to support a resident colony of predators like Nessie.
0:30:06 > 0:30:07< GURGLING
0:30:08 > 0:30:11Probably nothing.
0:30:13 > 0:30:18We've seen the importance of the rock to freshwater habitats.
0:30:18 > 0:30:23But the other reason Loch Ness is so devoid of life is because it's dark.
0:30:23 > 0:30:26The peat in the water makes great whisky,
0:30:26 > 0:30:31but its dark-brown stain means sunlight struggles through.
0:30:31 > 0:30:34And without light, not much can survive.
0:30:38 > 0:30:42The reason divers spend a fortune travelling to the Mediterranean or
0:30:42 > 0:30:48Red Sea is that the clear, shallow water lets in loads of light,
0:30:48 > 0:30:54encouraging plant life, which in turn supports the shoals of fish the divers come to enjoy.
0:30:58 > 0:31:00But this isn't the Med,
0:31:00 > 0:31:04this is Britain, and about as far from the sea as you could get.
0:31:06 > 0:31:10This is Stoney Cove, a flooded freshwater quarry
0:31:10 > 0:31:15in the heart of England's Midlands, and a national centre for diving.
0:31:15 > 0:31:21Cynical old sea dogs rather disparagingly call it the headquarters of the Birmingham navy.
0:31:23 > 0:31:26Now, granted, this is not the most exotic location
0:31:26 > 0:31:30I've ever brought you to, and this water is decidedly parky.
0:31:30 > 0:31:34But, believe me, down there there is something every bit as amazing
0:31:34 > 0:31:37as what you'd find on the Great Barrier Reef.
0:31:37 > 0:31:39Come on, follow me.
0:31:42 > 0:31:45Because large areas of the lake are shallow,
0:31:45 > 0:31:53sunlight can reach the bottom, allowing plants to grow, insects to flourish and fish to thrive.
0:31:54 > 0:32:00And where there are this many fish, you'll find one of freshwater Britain's top predators.
0:32:08 > 0:32:12If you didn't know this was freshwater, you'd think the fish
0:32:12 > 0:32:16cruising these wrecks were barracuda, but they're pike.
0:32:19 > 0:32:22Their ferocity is legendary.
0:32:22 > 0:32:29But for just a handful of days each year, perhaps only hours, they show a more sensitive side.
0:32:31 > 0:32:35And for the first time ever, we can share it with you.
0:32:40 > 0:32:48Even feared predators have to be parents, and in the spring, as the sunlight warms the water,
0:32:48 > 0:32:51these solitary hunters throw aside their differences
0:32:51 > 0:32:55and delicately woo their prospective partners.
0:32:57 > 0:32:59As the time nears to shed her eggs,
0:32:59 > 0:33:05the female resting in the reeds attracts a host of hopeful males.
0:33:13 > 0:33:16And when the attention gets too much,
0:33:16 > 0:33:20she leads an entourage around the lake...
0:33:24 > 0:33:30..each attentive male vying to be the perfect partner.
0:33:42 > 0:33:45The outcome - thousands of eggs.
0:33:49 > 0:33:53The young pike will hatch and grow, until one day they, too,
0:33:53 > 0:33:59will join the ranks of feared predators stalking Stoney Cove...
0:34:01 > 0:34:07..in waters made rich with prey by the sunlight.
0:34:07 > 0:34:11Well, it may not be the Med, but Britain's freshwater habitats
0:34:11 > 0:34:12can be every bit as beautiful,
0:34:12 > 0:34:16and our wildlife behaviour just as fascinating.
0:34:16 > 0:34:19But after a quick dip in there, I ain't half ready for a cup of tea.
0:34:19 > 0:34:23Thank you. I don't know whether to drink this or wear it.
0:34:23 > 0:34:24Cheers.
0:34:25 > 0:34:27Lovely.
0:34:27 > 0:34:29From the still waters of flooded quarries,
0:34:29 > 0:34:33let's join the river again, on its journey to the sea.
0:34:33 > 0:34:40We're off to East Anglia to visit a freshwater habitat that rivals the richest on Earth.
0:34:40 > 0:34:47And that means there's one animal that can thrive in greater numbers here than anywhere else.
0:34:48 > 0:34:53This is its nest, but it's not made by a bird...
0:34:54 > 0:34:56..it's made by a mammal.
0:34:58 > 0:35:02And high in the reeds you'll find its newborn babies.
0:35:09 > 0:35:12Each one is the size of a raisin.
0:35:12 > 0:35:17The whole litter weighs less than a tuppenny piece.
0:35:20 > 0:35:25When they're born, their eyes are closed to the dangers that lurk outside.
0:35:25 > 0:35:31Their days are spent resting, perhaps dreaming, while their mother keeps them warm.
0:35:34 > 0:35:40At just eight days old, they've grown fur and opened their eyes.
0:35:45 > 0:35:48But it'll soon be time to leave this sanctuary.
0:35:51 > 0:35:55At just two weeks old, they clamber up into the reeds
0:35:55 > 0:36:01for the very first time, to face the big, wide, world.
0:36:01 > 0:36:04And what a world!
0:36:07 > 0:36:08Crowded with people.
0:36:13 > 0:36:17And with powerful predators lurking just beneath the surface.
0:36:21 > 0:36:24These are the Norfolk Broads.
0:36:28 > 0:36:29And the mammal?
0:36:29 > 0:36:34The commonest among the reeds isn't a water shrew, or a water vole,
0:36:34 > 0:36:39but a harvest mouse, not only a farmland creature,
0:36:39 > 0:36:41but a freshwater one.
0:36:43 > 0:36:46These are the smallest rodents in Europe.
0:36:46 > 0:36:50Even fully grown they can be as little as a couple of inches long.
0:36:54 > 0:36:56They're superb climbers,
0:36:56 > 0:37:00possessing something not one African monkey can boast -
0:37:00 > 0:37:03a truly prehensile tail.
0:37:03 > 0:37:07It allows them to clamber to the very tops of the reeds,
0:37:07 > 0:37:09where they feed on the seeds.
0:37:09 > 0:37:15It's these climbing skills that make the harvest mouse at home in our farmland crops.
0:37:15 > 0:37:18But it does even better here among the reeds.
0:37:21 > 0:37:25And it's the reeds that make this freshwater habitat so productive.
0:37:29 > 0:37:35We've seen how the river's speed gives it the energy to pick up and sweep along nutrients.
0:37:35 > 0:37:40But wherever it slows, it no longer has the strength to carry them.
0:37:41 > 0:37:48These reeds act like a huge brake, slowing down the river and forcing it to drop its cargo.
0:37:48 > 0:37:52As a result, reeds are among the fastest growing plants on Earth.
0:37:52 > 0:37:58They make these wetlands almost as productive as a tropical rain forest.
0:38:02 > 0:38:07It's the perfect place to hide one of our strangest creatures.
0:38:13 > 0:38:19For thousands of years, this has been a place of mystery.
0:38:19 > 0:38:21It's almost prehistoric.
0:38:32 > 0:38:38So perhaps it's no wonder that tusked beasts still roam the reeds.
0:38:48 > 0:38:51These are Chinese water deer.
0:38:51 > 0:38:55In their native China, they're so rare that Chinese scientists wanting
0:38:55 > 0:38:59to learn more about them came to Britain to study them instead.
0:39:02 > 0:39:08They're considered rather primitive, having no antlers, only tusks,
0:39:08 > 0:39:11sported by both the males and females.
0:39:15 > 0:39:20They're solitary for most of the year, but come December, the time of the rut,
0:39:20 > 0:39:27they stake out their territories, marking the boundaries with scent from a special gland on their face.
0:39:31 > 0:39:35When you lead such a secretive life, these scented messages
0:39:35 > 0:39:40can be read by others for days, warning them to steer clear.
0:39:40 > 0:39:43But some males just don't get the message.
0:39:43 > 0:39:47Those tusks aren't just for show, you know.
0:40:14 > 0:40:19This tangled forest of reeds means it can be really hard to find anyone.
0:40:19 > 0:40:25The deer may leave scented messages, but the birds have another solution.
0:40:25 > 0:40:27WARBLING
0:40:27 > 0:40:29That's how they do it. Did you hear that?
0:40:29 > 0:40:31That chug, chug, chug, chukachukachuk.
0:40:31 > 0:40:36A reed warbler, which has come over here from Africa to nest.
0:40:36 > 0:40:38And like all birds that live in reeds
0:40:38 > 0:40:44and tall undergrowth like this, it needs a loud and penetrating call to advertise its presence.
0:40:44 > 0:40:50But in so doing, it lays itself open to outrageous deception.
0:40:52 > 0:40:57Carefully woven into the reeds is the reed warbler's nest,
0:40:57 > 0:41:01and inside, the first chick has already hatched.
0:41:06 > 0:41:12It's weak and helpless, until its mother's back is turned.
0:41:48 > 0:41:54The parent looks on, seemingly in disbelief.
0:41:54 > 0:41:59This isn't normal for a young reed warbler.
0:41:59 > 0:42:02But blind to junior's behavioural problems,
0:42:02 > 0:42:06like all good parents Mum and Dad work from dawn to dusk
0:42:06 > 0:42:10to provide for what's now their only child.
0:42:10 > 0:42:16Who is perhaps growing a little overweight on all their attention.
0:42:19 > 0:42:25The parents, as always, seem to be the last to realise.
0:42:25 > 0:42:29Until one day, surely even they can't deny
0:42:29 > 0:42:32that a terrible mistake has been made.
0:42:37 > 0:42:41Of course, this isn't a reed warbler at all.
0:42:41 > 0:42:43It's a cuckoo.
0:42:43 > 0:42:49It would be wrong to judge the cuckoo's life of deception by our standards.
0:42:49 > 0:42:52But if you did, I'd blame the parents.
0:42:54 > 0:42:58After laying its egg in as little as ten seconds,
0:42:58 > 0:43:01its mother deserted and upped sticks to Africa.
0:43:01 > 0:43:07The young cuckoo will never meet Mum and Dad, and has to make the long journey south alone.
0:43:07 > 0:43:09IT CUCKOOS
0:43:09 > 0:43:14Despite their skill, cuckoo numbers are in decline.
0:43:14 > 0:43:19But not here. Reed warblers, unlike other cuckoo hosts, are doing well.
0:43:19 > 0:43:23So this is one of the few places where the cuckoos are sure to find
0:43:23 > 0:43:28enough surrogate parents to make the long journey from Africa worthwhile.
0:43:30 > 0:43:33The dumping of the river's nutrient cargo
0:43:33 > 0:43:40doesn't just happen in reed beds, it occurs wherever the river slows,
0:43:40 > 0:43:44and there's one habitat it creates that's so lush
0:43:44 > 0:43:48it tempts one winter visitor hundreds of miles across the ocean.
0:44:00 > 0:44:05Every year, thousands of whooper swans travel to Britain from Iceland.
0:44:19 > 0:44:24And it's here that most of them come - the Ouse Washes of East Anglia.
0:44:28 > 0:44:32As rivers near the flatter areas toward the coast,
0:44:32 > 0:44:36they slow, spread out, and can flood the low-lying land.
0:44:41 > 0:44:45This is the biggest area of flooded grassland in Britain,
0:44:45 > 0:44:48and the swans come here in their thousands,
0:44:48 > 0:44:53taking advantage of grass growing lush due to the seasonal floods.
0:44:55 > 0:44:58THEY HONK
0:44:58 > 0:45:01It's the freshwater that attracts the whoopers,
0:45:01 > 0:45:06and thousands of other birds, from as far away as Arctic Russia,
0:45:06 > 0:45:12making this not just one of the most important areas for birds in Britain,
0:45:12 > 0:45:14but in the world.
0:45:29 > 0:45:36From the Ouse Washes, it's just a few miles to the end of the river's journey,
0:45:36 > 0:45:37and ours.
0:45:39 > 0:45:42We've finally reached the sea.
0:45:44 > 0:45:51This is the Wash - one of the biggest estuaries in Britain, and a favourite holiday destination.
0:45:54 > 0:45:58But I wonder how many of the sun- seekers along this stretch of coast
0:45:58 > 0:46:04realise that it's freshwater that makes this such a special place?
0:46:04 > 0:46:06Not now,
0:46:06 > 0:46:08but in the depths of winter.
0:46:12 > 0:46:16For a drop of freshwater heading downstream,
0:46:16 > 0:46:19the seaside marks the end of the ride.
0:46:19 > 0:46:26All that playful tumbling over rocks and rapids, and the gliding lazily by grassy banks is over.
0:46:26 > 0:46:33The coast is the start of a new life, as part of something much bigger - the ocean.
0:46:36 > 0:46:43But before embarking on this new adventure, the river has one last thing to do.
0:46:43 > 0:46:48Ever since it first began to flow, it's toyed with sand and silt,
0:46:48 > 0:46:52carried it from far inland.
0:46:52 > 0:46:55But at the coast, as it comes of age,
0:46:55 > 0:47:01it leaves those play things behind, creating the estuary.
0:47:01 > 0:47:07And drawn here, every winter, are huge flocks of wading birds that swirl in the sky.
0:47:10 > 0:47:13But that's a different story.
0:47:13 > 0:47:15Our journey is over,
0:47:15 > 0:47:21a journey that started with a single drop of rain.
0:47:21 > 0:47:25So the next time you raise your eyes to the heavens
0:47:25 > 0:47:30and see rain clouds building on the horizon, don't be downhearted.
0:47:30 > 0:47:35Remember that it's rain that supplies the kingfisher with food
0:47:35 > 0:47:38and allows the salmon to swim upstream.
0:47:38 > 0:47:42It's rain that keeps the damselflies dancing
0:47:42 > 0:47:45and the Loch Ness legend alive.
0:47:45 > 0:47:50Every last drop brings life to the land and, for me,
0:47:50 > 0:47:53it seems that that is a small price to pay
0:47:53 > 0:47:55for getting a little bit damp.