Original subtitles

SQUAWKING

A reed-bed in Somerset,

and dragonflies glint in the early morning sun.

They won't take to the air until their wings are dry.

Others have spent the night in large communal roosts...

...and, as the day warms, they slowly climb up the reeds.

Until finally...

...they're ready.

All dragonflies begin their lives as larvae in freshwater

before emerging as adults for their summer in the sun.

Their flying agility is second to none.

Or almost none.

A hobby.

These small birds of prey spend the winter in Africa

and time their arrival in Britain

to take advantage of this mass emergence of dragonflies.

But things don't always go their way.

The dragonflies can dodge with a flick of their wings...

...so the hobbies turn their attention to the female dragonflies,

who are busy laying their eggs on the water's surface.

The hobbies come in low and fast.

Got her!

This summer spectacle is totally dependent on one thing.

Freshwater.

Here in Britain and Ireland,

we have some of the loveliest rivers and lakes in the world.

From the lochs of Scotland to the waterfalls of Wales.

From the great Shannon River in Ireland

to small intimate chalk streams like this one in Wiltshire.

But today, less than half of our rivers and lakes

are in good health for nature.

In this episode, we will reveal the crucial role that freshwater plays

in supporting wildlife of all kinds.

Freshwater is the lifeblood of the natural world.

We have over 150,000 miles of rivers in the British Isles.

They flow through every landscape, connecting all our wildlife.

The water's journey starts at the top of the mountains.

Rivers shape the landscape.

They feed and water a multitude of different habitats.

And, finally, they enter the sea.

And here in northern Scotland,

ghostly shadows have gathered where they do so.

Atlantic salmon.

After four years at sea, they've returned to the very river

where they were hatched.

It's spring, and they will spend the next six-months

battling their way up-river to their breeding ground.

But their great numbers have attracted attention.

Bottlenose dolphins.

A pod has gathered at the mouth of the River Ness.

The tide is rising, and this is when the fish

will try to enter the river itself.

The salmon may be over a metre long and difficult to swallow...

...but these intelligent hunters still find time

to play with their food.

Those salmon that get past them swim through a hazy mix of waters...

...and at last reach the fresh.

From this point on, they are freshwater fish.

Their bodies change, inside and out.

Their sea-fresh silvery sheen dulls to a darker hue

that camouflages them against the riverbed.

But the river is low.

Until there's rain, they can go no further.

They may be stuck here for months.

As they will no longer eat, conserving energy is key.

Rain - at last.

The river rises, so the fish can start moving further upstream.

The rapids of the lowlands are passed without much effort.

But things soon start to get more difficult.

The salmon push on ever higher,

before reaching the most demanding test on their journey.

These falls are three metres high...

...and right at the fish's limits.

They gather beneath the thundering water.

Some make practice leaps...

...assessing the best angles of attack.

Finally, the time is right...

...and now the real leaping begins.

They use the white water to slingshot their bodies into the air.

No other fish can clear waterfalls as high as this one.

Some crash into the rocks,

the thud of their muscular bodies audible

even above the roar of the water.

Every year, fewer and fewer get to this point in the river.

Returning salmon numbers have fallen by 70%

in just 25 years.

But those that have got here push on with astonishing vigour.

By late autumn, the survivors finally arrive

at their traditional spawning grounds.

It's time, at last, to breed.

The females get straight to work, digging their redds -

shallow depressions in the gravel.

This is where they will lay their eggs.

The males, in full spawning colours

and with newly-developed hooked jaws, wait close by.

A female releases thousands of eggs...

...and one of the males fertilises them as they emerge.

It's the culmination of a journey

against the flow and the odds.

The eggs will develop in the gravel throughout the winter

and soon become tiny fry.

Their heartbeats visible through their translucent skin.

The salmon's return will sustain the whole river ecosystem

through the long winter months.

But they need cold, clear, free-flowing water to thrive,

and due to climate change, pollution and dams,

all are in short supply.

Atlantic salmon were once common across Britain and Ireland,

but are now increasingly restricted to these remote northern rivers.

At the current rate of decline, they may disappear

from all our rivers in as little as 20 years' time.

The grandchildren of these fish may be the last

to make this astonishing journey.

The rivers, having left the mountains, widen and slacken.

In places, they enter lakes such as this loch in Perthshire.

But here something else may slow them.

Beavers.

400 years ago, they were hunted to extinction for their fur,

but now they've been reintroduced to Scotland

and it hasn't taken them long to get established.

Signs of their industry are easy to see.

They are best known, perhaps, for their skill in building dams,

and this family spends a lot of time making sure that theirs

is in good shape.

The dam has created a huge wetland.

It's a beaver-built paradise...

...that provides plenty of living space

and unlimited access to food.

At this time of year, branches on the move can only mean one thing.

Newborn beaver kits.

The kits will stay with their family for the first few years,

before setting out to find territories of their own.

There are over 250 beaver territories in Scotland,

and they're now being reintroduced into England and Wales.

By slowing the river, the beavers create a rich habitat

for a whole range of other species.

Right to the top of the food chain.

Ospreys.

Still, clean water attracts all kinds of wildlife.

On a heathland in Dorset,

spiders' webs cover the bushes surrounding a pond.

And one specialist species lives at the very edge of the water.

A female raft spider.

She's the size of your palm and a deadly assassin.

She uses the surface of the water as her web...

...and senses the presence of prey from its vibrations.

A good start, but it's mating season,

and she'll need much more food if she's going to breed.

A pond-skater could be a good snack.

But it's not easily caught.

Such a small meal is barely worth the effort...

...but she can also hunt under the surface.

There are much bigger meals to be had down here.

The larva of a diving-beetle.

Itself a ferocious predator.

But it has to come to the surface to breathe

through a tube in its rear.

And that brings it within striking range of the spider.

At last, a real meal.

Now she has the energy needed to find a mate.

She lays down a thread of silk

laced with perfume...

...before returning to her favourite spot.

And it's not long before another raft spider picks up the trail.

A male.

He has a pair of large boxing glove-like organs

called pedipalps in which he stores his sperm.

And this is what he's been looking for -

a thread of silk that leads straight to her.

Once close, he taps the water's surface

to signal that he's about to approach.

He's no bigger than her last meal.

A wrong move now and he could become dessert.

She seems receptive.

It's now or never.

Carefully does it.

They mate in a tangle of legs

and he uses one of his palps to transfer his sperm

into a sac in her body, where she will keep it

until she's ready to use it.

The male then beats a hasty retreat...

...before she makes a meal of him, too.

As rivers reach the middle stages of their journey,

they increase in both size and power.

And it is their force over millennia that has shaped our landscape.

In limestone country,

the freshwater carves its way underground.

Britain and Ireland contain thousands of miles of caves,

including these in County Cavan.

The dripping water builds stalactites and stalagmites,

like these teeth coming together in a rocky grimace.

Over centuries, it can create all kinds of pillars and curtains.

Yet, even here, there is life.

CLICKING

Daubenton's bats roost in caves during the day.

And, as night falls, they head out to feed.

Ghostly shapes appear over a starlit river.

The bats navigate by sending out echolocation calls

which we can watch in operation if we slow down both sound and picture.

It's soon clear why Daubenton's bats

are also called water bats.

They patrol the river, searching for tiny movements on the surface

of the slow-moving water.

They use the echoes from their calls...

CLICKING

...to lock on to their prey.

And then skim it from the surface.

Weighing about 8g, these little bats can nearly double

their body weight in a single night's hunting.

And on this autumn night,

the males in particular need all the energy they can get.

A Daubenton's bat circles in a woodland glade.

And it's soon joined by others emerging from a cave

at the base of a tree.

Amongst their navigational clicks, there's a different sound.

CHIRPING

They are calling to one another.

CHIRPING

As their numbers increase, so do their calls.

Soon, other species arrive, including Natterer's

and brown long-eared bats.

There can be up to ten species at any one time,

whirling around in this pitch-black arena.

This is a display ground

where male bats compete to impress the females.

Some of these bats have travelled over 40 miles to be here.

CHIRPING

Around midnight, the bats disappear back into the caves below,

where they will soon settle down to hibernate.

Spring brings the end of hibernation for another animal.

CROAKING

A common toad.

This is a female.

Common toads need freshwater in which to lay their eggs,

so she must find a pond...

...and that can involve a journey of several miles

which is full of obstacles and dangers.

She's not the only one on the move tonight.

Male toads are also about.

They're in search of females,

and when this male finds one, he locks on tight.

But his rivals have the same idea...

...and then it's a wet-legged wrestling match

to stay in prime position.

The competition is seen off and the bonus is a free ride.

But the biggest challenge lies ahead.

Roads now cross many of the toads' traditional migration routes

and tens of thousands are killed every year.

CROAKING

Made it.

With toad numbers down by two-thirds

in the past 30 years,

we ought to be careful on warm, wet nights in March.

At dawn, the female and her hitchhiker

reach the end of their journey.

The very pond in which she hatched as a tadpole.

They get straight down to business

and the female produces thousands of eggs in long links of spawn.

The male, if he holds on tight, will fertilise them all.

A few months later and summer is here.

These tiny toadlets are now ready for their next stage.

They must head for dry land.

They will spend most of their adult lives in the woods

from which their mother emerged.

But to get there, they must cross a killing zone...

...haunted by giant leeches.

Some are 15cm long.

And they have an appetite for baby toads.

They hunt using a keen sense of smell and five pairs of eyes.

The toadlets must keep going if they want to reach the woods.

If they're not quick enough, their fate is grim.

Consumed whole.

SQUEAKING

The leeches can grab with either end of their body

and three sets of teeth.

Once caught, a toadlet has no escape.

But for every one that is taken,

hundreds make it to the safety of the woods.

For most of these toadlets, it's a horror story with a happy end.

In the British Isles, we have one of the world's rarest

and most beautiful freshwater habitats.

Chalk streams.

Only around 200 exist in the world

and over three-quarters of those flow here in England.

A reliable flow of cool, mineral-rich water

bubbles up through the chalk below

and supports a rich freshwater community.

SQUAWKING

On the riverbed, something stirs.

This young insect has spent the last two years

buried in the gravel.

With strong front legs, feathery gills and a stream-lined body,

it's excellently adapted to life underwater.

But it's late May, and everything is about to change.

Even breaking through the surface is a challenge

when you're just 2cm long.

Finally, as its wings unfurl,

the little creature starts a new life as an adult -

a male mayfly.

He now has just a few short days to live,

so he quickly prepares for his first flight.

And the sooner the better.

The fish below are the first to notice this springtime bonanza.

And it's not long before those above water also get their eye in.

He needs to get airborne.

But it's out of the frying pan

and into the fire.

At least the mayfly have the advantage of great numbers.

In just a week, more than a million will emerge

from this stretch of river alone.

And the first thing the male does is head for the river bank.

Unique among insects, mayfly undergo a second adult moult

before they're fully mature.

His whole life has been building to this moment.

And finally, he's ready.

He flies high above the river

and joins the mating dance.

Rising and falling with the other males,

he spreads out his tail, showing off his aerial prowess.

It's all for the benefit of the females,

who are now emerging from the water below.

Soon, the river bank is alive with mating pairs.

Each male will continue to dance until he dies of exhaustion.

A small hole in the river bank -

home to one of the most secretive of the river's residents.

A shrew.

This one, a female,

is pretty small - about the size of your thumb.

Being small means she loses heat quickly

and must eat almost constantly.

Three hours without food could be fatal...

...so when supplies on the bank get low,

she must find food elsewhere.

She's a water shrew.

She's somewhat reluctant at first.

Underwater, she will lose heat even faster.

But needs must, so when she does take the plunge,

she works at great speed.

In real time, it's impossible to see what's going on.

But slowing things down reveals how marvellously adapted she is

to the underwater world.

Stiff hairs on her feet act like flippers

and others on her tail turn it into a rudder.

She swims with her eyes closed...

...fanning out her whiskers to help her sense her prey.

And, most remarkably,

she can detect smells down here.

She lets out tiny bubbles of air

to pick up scent particles in the water.

It's known as bubble sniffing.

But using this technique means she quickly runs out of air.

This time, everything comes together.

A dragonfly larva is a huge meal

but hard to subdue.

It's time to use her final weapon.

Water shrews are the only mammal in Britain with venomous saliva.

All wildlife is dependent, to some extent, on freshwater.

But here in England, every single river is polluted.

Run-off from farming and dumping of human waste

causes algae to bloom.

This reduces oxygen, chokes the plants,

and degrades the rivers on which our wildlife depends.

GRUNTING

As rivers approach the end of their journeys, they slow,

and beds of reeds are able to take root.

Here in Suffolk, it's late winter.

Red deer.

This huge area is a little-known winter refuge

for Britain's largest land mammal.

The paths the deer create make gaps in the reeds.

And on the open water,

great crested grebes.

It may be early in the year,

but their mating dance is already well under way.

As a prologue, the birds shake their heads,

showing off their plumage and preening

to make sure their feathers are in tiptop condition.

Costumes ready, act one reaffirms any bonds

that were made in previous years.

Single birds call for a partner...

...before adopting a posture known as the cat display.

It's an invitation...

...for a duet.

It seems to have been accepted.

The pair are falling into step.

But they are interrupted by a rival.

SQUAWKING

Another male is looking for a partner

and starts a sharp-beaked argument.

But all's well that ends well.

The rival is seen off

and the pair begin the final act of their duet -

the weed dance.

These complex displays create a bond between the pair

which will keep the two together as they raise their young.

A few weeks later, and the first chick appears,

shortly followed by the second.

Both parents care for the chicks, taking turns to babysit

while the other finds food.

CHIRPING

They even take feathers from their own backs

and feed them to the chicks

to protect tiny tummies from sharp fish bones.

This extraordinary caring behaviour

depends on the firm bonds that were made back in the spring.

Grebes that dance together stay together.

We have lost huge areas of reedbeds over the years,

drained for agriculture.

But recent conservation efforts have shown that they can be restored

remarkably quickly.

The journey of freshwater ends when rivers reach the sea.

Here they may create vast mudflats.

Together, they constitute over 2,000 square miles

of our coastline.

From above, they look lifeless.

But they are full of opportunities.

It's low tide, and there is plenty of space to forage.

Every winter, millions of migratory birds from all over

the northern hemisphere arrive in our estuaries to refuel.

But the tide has turned and the sea starts rushing in.

The restaurant is closing

and the birds are driven from the mud.

The most common birds here - knot, take to the air en masse.

Watching from above, a peregrine.

It may be the fastest animal on the planet,

but it won't be rushed.

It surveys the flock from on high...

...and then tucks in its wings

and dives at speeds of up to 200mph.

The knot bunch tightly together.

There's safety in the middle of the flock.

It's difficult for the peregrine to select an individual bird...

...so it changes its tactics.

Coming in low, it's easier to pick out an individual knot.

Using the hard-packed mud as a weapon,

it drives its victim into the ground.

The knot is left with a damaged wing.

But the peregrine will be back.

Every winter, peregrines come to the coasts of the British Isles

to take advantage of this seasonal bounty.

The flock is reduced by one...

...but when you are 100,000 strong,

that is a small price to pay.

With the tide now at its highest,

the birds settle down to rest.

The position of the British Isles on the planet

makes our estuaries globally important.

SQUAWKING

They provide vital refuelling stations for migratory birds

from different parts of the globe.

On its journey from the mountains to the sea,

freshwater has fed and refreshed the natural world.

It's the lifeblood of our Wild Isles.

One of the greatest spectacles

in the British Isles

is the migration of Atlantic Salmon.

Despite their numbers being in freefall,

the freshwater team were determined to find new ways

to film these astonishing fish.

Their story begins near Inverness in north-east Scotland.

Every summer, a pod of bottlenose dolphins gather just offshore,

drawn here by the salmon.

They come along a very narrow channel that runs

just off the beach here.

The dolphins have clocked that

and they can basically just sit off the point in this deep channel

and wait for the fish to come and just pick them off.

The dolphins only hunt for about an hour,

so the crew get into position early.

But they're not the only ones.

Crowds of people soon join to see the action.

This is one of the best places in the world

to see this behaviour so close to shore.

The next stage for the salmon is to swim up into the freshwater.

Here, they're nervous and extremely wary of people,

so it's almost impossible to film using standard techniques.

But the crew have a trick up their sleeves.

An underwater drone.

This is another, "What could possibly go wrong?" moment.

HE LAUGHS

Taff has been experimenting with this technology for over five years

and thinks it's the only way to really enter the salmon's world.

Even now, it doesn't always go to plan.

Oh!

Ah, no, one of the screws has gone.

There is no way I'm going to find the screw.

Oh, oh, oh! What?!

Oh, you beauty.

With the sub back up and running,

the team begin to record the salmon's underwater world.

A glimpse into this extraordinary migration

that few people have seen.

One of the most beautiful things I've ever seen.

Absolutely mesmerising.

The next and greatest challenge for the salmon

is ascending the three-metre waterfall.

Filming the salmon leaping here is the team's biggest challenge, too.

For the first shot, the camera needs to be positioned

directly above the falls.

That means getting more than 100kg of kit into position

four metres above the roaring water.

The fish still aren't jumping at the moment,

but that's fine cos they're waiting for the water to drop.

Hopefully, in the next few hours, they'll start to jump

and once they do start, there should be repeated attempts of this.

The new camera position pays off.

The team film the salmon leaping head-on for the first time.

But there's one angle that Taff has been dreaming about for years.

We're going to try the dream shot -

the fish actually leaving the water from below.

OK, so this is it. The moment of truth

OK. Yeah, yeah, I'm ready.

Yeah.

Away she goes.

Below the falls, the water flow is at its highest...

...putting the sub and Taff's skills under serious pressure.

You know, probably nobody's watched this behaviour,

but they nervously go and look at it, and then they go around

and they do a little test and then they come back

and then they go for it. Absolutely amazing.

All these years filming salmon, it's the first time I've seen this.

This was the first time salmon had been filmed leaping from underwater.

Finally, just a few salmon make it to the top of the river.

The place in the river where they themselves hatched as young salmon.

When breeding, they are at their most sensitive,

and getting these intimate moments needs some serious dedication.

I'll film every day other than Christmas Day and Boxing Day

and I would film on Christmas Day if my wife would let me,

but she does not let me do that.

I've been doing this for about five years,

so we know when and where the fish are going to spawn now.

So, that's the key thing - is knowing where they are.

With spawning complete, the salmon's journey is done.

But for the crew, there's one final part of the story.

And they've waited three years for the perfect conditions.

Not a very elegant slide,

but this is a really cool slide.

An otter slide.

A clear indication there's one nearby.

Otters are usually very elusive during the day.

These cold conditions gave Raymond his chance.

I can see the otter further downriver.

It's just come out onto the ice shelf on the side there.

It's only staying for, like, three or four seconds,

then it's back in the water.

It's hard work, this.

At the very end of their journey, the salmon not only provide

a much-needed meal for this otter,

their dying bodies will provide essential nutrients,

enriching the upper reaches of our rivers.

Salmon once swam in rivers throughout the British Isles

in huge numbers, but in the last 25 years

the number returning from the sea has dropped by 70%.

In England and Wales, the situation is critical,

with over 90% of salmon river populations at risk of collapse.

Having filmed them in all these different places

and all these different environments,

it's really brought home that, you know,

we really are messing with them every step of the way.

Our man-made barriers block their migration routes.

Sewage from towns and cities

and agricultural run-off from farms pollute our rivers,

making the salmon more susceptible to disease.

On top of all this, climate change presents them

with even greater challenges.

They need cold, clean water. That's what they need.

And a lot of areas, they're not getting that.

Anything over 23 degrees, they stop feeding,

and anything over 30, they die within minutes.

We need to look at trying to manage those water temperatures.

And if we can bring that habitat back -

in effect, rewild those bits of rivers to put them

to how they should historically have been, it's going to have

a knock-on benefit for all the species that use the ecosystem.

Salmon are resilient animals.

If we can improve the quality of our freshwater,

remove barriers to its flow

and better manage the challenges at sea...

...salmon could once more become abundant

across the British Isles.

Next time - our ocean.

A hidden world...

...full of colour...

...and surprise.

The Open University has produced a free poster

exploring our wild isles and their diverse habitats and species.

Order your copy by calling 0300 303 0265

or go to bbc.co.uk/wildisles

and follow the links through the Open University.

If you'd like to play your part in restoring our wild isles

and learn more about what you can do to help,

just search Wild Isles on the BBC website.

The Open University has produced an interactive map

exploring our wild isles

and their diverse habitats and species.

Go to bbc.co.uk/wildisles

and follow the links to The Open University

to find out more.

If you would like to play your part in restoring our wild isles,

and learn more about what you can do to help,

just search Wild Isles on the BBC website.