Botswana Swimming with Crocodiles

Crocodiles have roamed the earth for over 100 million years.

Yet much of their lives remain a mystery.

Look at the size of that crocodile there!

These giant reptiles kill hundreds of people in Africa every year.

That was really quick. That was like a gun!

To help reduce attacks, we need to understand their behaviour.

30 centimetres below him, watching him, and it just snapped...

-Snapped on the camera.

-It was ridiculous.

So I'm in Botswana, joining a research team who,

for the first time ever, will attempt to study them underwater.

Three, two, one.

If successful, the expedition could revolutionise our understanding

of these majestic creatures.

Holy crap.

This has got to be one of the most extraordinary encounters

I've ever had.

But it's a challenge fraught with risk.

They attacked you?

Right from behind. Came right behind us.

I had to use the camera, it got the bloody light in its mouth.

That's kind of totally thrown me.

I've come to Botswana's Okavango Delta in southern Africa.

It's a massive wetland the size of Switzerland

and home to Africa's Nile crocodile.

Like most people, I know very little about crocodiles.

But I'm about to get a unique insight into their behaviour.

-I'm Ben, very nice to see you. How are you?

-Pleased to meet you.

-Thank you very much.

-Need a hand?

-That would be great.

'For the next ten days, I'll be working on a groundbreaking project

'with a team pioneering the study of wild crocodiles underwater.'

It still, to me, seems slightly ridiculous

that I'm actually going in the water with crocodiles.

But, you know, right now, I've still got my getting-in-the-water hat on.

'The core diving team will be based here at Nxamaseri Lodge.'

-Hey.

-Hey.

'In the heart of one of Africa's richest areas of natural wildlife.'

Nice spot for a lodge. Could it be any remoter?

-Nice to meet you.

-Nice to meet you. Andy.

-How are you?

-Good, thanks.

It's beautiful. How long have you been here?

'Once I've dropped off my bags and before we begin our study proper,'

I head out onto the water with one of our team

for my first encounter with a Nile crocodile.

We have crocodiles all around us,

but the ones we're going to see are going to be the adults, most likely.

And we get quite a few adults in this section of the river.

If we're lucky we'll see a nice big, four-metre.

'Ecologist Vince Shacks

'has been monitoring the local crocodile population for the last seven years.'

-There we go, there we go.

-Is it this one here?

Yeah.

Wow. That's a big croc!

So what sort of size do you think that is?

It's around three metres. Yeah. Maybe even three-and-a-half.

'Nile crocodiles can grow up to six metres and weigh as much as a car.

'Some live to be 100 years old.'

-Look at those teeth!

-Adults normally start losing their teeth

and losing a lot of condition in their teeth at this sort of age,

so it's in pretty good shape.

Got a nice, big, fat neck. Big, bulky head.

When the adults get old, they start getting really gnarly features.

All the bones start popping out.

-Already, this is the closest I've ever been to a crocodile.

-OK.

They are extraordinary looking things, aren't they?

And ooh, look, look, look, here it goes!

That's quick!

Wow, that's a bit disconcerting! Is it under us, then?

-It'll be straight underneath us, yeah.

-We can't see it.

-Yeah, it's pretty murky there.

-Gone.

It'll come down and sneak into the shadows over here and sit still.

-Yeah.

-Very calmly wait for us to leave.

-And then take up its position again?

-Get back up again, yeah.

-Wow!

Oh, look at that!

These crocodiles spend around 80% of their lives submerged.

Woah!

'Until the 1970s, crocodiles here were hunted for their skins.'

-They really blend in.

-They really do that, they really do.

There in the water, that's it, it's gone.

'But since the practice was outlawed,

'numbers have rallied in the Delta Panhandle to over 3,000.'

Can you tell, by looking at a crocodile from that distance,

maybe, do you recognise indiv...

-If you recognise it.

-I thought that was a crocodile!

-That's how jumpy I am!

-Let's just get out of here.

It does, it makes you jumpy, we're out here...

It does, like, everywhere.

'Vince's job is to monitor the health of the crocodile population.

'And his research methods couldn't be more hands on.'

Woah, you caught it! Oh, my God!

You're like Crocodile Dundee!

This is just small, so obviously the size we're looking for is a lot bigger than this.

But it's probably a good time to just let you grasp the animal

-and get used to it.

-Grasp the animal? Yeah, OK.

-Yeah, you can have...

-What size is this?

-Oh, this is probably about 80 centimetres.

See, so if I let the jaws relax and they just open,

kind of getting ready to bite anything.

-If you want to just grab...

-Yeah.

-Grab the jaws first. The head there.

-You'll feel the top of the...

-Yeah, it's powerful.

-Just like that.

-Wow!

-You've got those jaws?

-Just about.

'Full grown crocodiles have the strongest bite of any reptile

'on Earth. More powerful than a T-rex.

'But you can hold their jaws shut surprisingly easily.'

I'm holding a crocodile.

OK, I admit it's quite small.

-Look, its jaw's opening, is that OK?

-As soon as you ease the pressure...

-Oh, yeah!

-You see you can close it very easily.

-Hello.

-Yeah.

What he's trying to do is he's trying to open and get ready for a bite.

These are the scutes that we use to mark the animal with, so these

are the ones that we'll cut off of the larger animals to identify them.

They act as a fingerprint because the patterns here are unique

to every crocodile.

You did that with your hands!

Wow! That's a bit bigger!

It's a bit bigger. Right, then.

OK, here's some tape, yeah, here we go.

That is a big... You got him?

Yeah.

What sort of size do you think this is?

It's probably a 1.2, 1.2 metres?

-That's all you're going to do his mouth with?

-Yeah.

-A piece of Sellotape.

-The tail scutes are still intact,

so this animal's never been caught before.

So yeah, he is a new guy.

And what sort of age do you think this one is?

-Wow! It's an amazing noise they make.

-It is, yeah.

Very low pitched growl.

CROCODILE GROWLS

He's basically just filling his lungs up to prepare to do something.

As we head for home,

I catch a glimpse of a huge crocodile under our boat.

-It's moving, it's moving, it's moving!

-Yeah.

See his head there?

Oh, my God, look at the size of that!

I have actually got goosebumps all up and down my arms.

-It's unbelievable.

-Unbelievable.

-I've never seen a crocodile like that underwater.

-Yeah.

'It's sobering to think we'll be diving with crocodiles this size

'and much bigger.

'Back at Nxamasari Lodge, I meet up with the team that I'll dive with

'for the next ten days -

'husband and wife, Brad Bestelink and Andy Crawford.

'Both expert divers and wildlife photographers.

'Leading this pilot research will be British zoologist Dr Adam Britton.

'This will be Adam's first chance

'to study wild crocodiles underwater.'

This is like a marriage made in heaven.

You've got the two first crocodile divers,

and Adam, you're pretty much the world expert on crocodiles.

I have wanted to do what you guys are doing for years,

because I thought to myself, "Look, these crocodiles,

"people misinterpret them, they misunderstand them.

"They're not the animals people think they are."

We're familiar with what they do underwater,

but we don't know the science behind why, you know,

and it opened our eyes to how we can work with them underwater.

I'm very nervous about this. I mean, I will... Yeah.

-I have genuine nerves now.

-Yeah.

But you should be apprehensive. It's completely normal.

I mean, I am a little bit apprehensive, to be honest.

I'm also incredibly excited and that tends to override it

but, at the same time, there's always that little inkling of fear

in the back of your mind thinking, "What if they're wrong?"

or, "What if this is the one time when it doesn't go to plan?"

That's why we're so strict on the safety

and, just, we're relying very much on crocs being what they are.

As long as we can minimise ourselves posing as a prey species,

that's going to increase our chances of having great interactions.

So presumably, the first thing is to get us in the water?

Yeah. You've got to get in the water, that's right, today.

-Today?

-Today. This afternoon.

-In here, Brad, this one?

-Yep.

Don't forget the sunblock and the hat.

Before we go anywhere near a crocodile,

I need to get used to the unique diving conditions

in the Okavango Delta.

We head out along the main channel to look for a spot

that's crocodile-free.

Hold on, guys! Hold on, there's an elephant!

-There's an elephant in the reeds, there.

-Elephant!

There's two.

I mean, if there's anything that reminds you we're in the middle of Africa now...

You get desensitised. Here we are on a river,

and suddenly you come across two elephants. Wow.

Brad and Andy became croc divers by accident.

They came across one unexpectedly while making a wildlife film

in these waters and were astonished when it didn't attack.

-Yeah, big one.

-Wow, it's a big one!

Since then, they've developed a system

to dive with Nile crocodiles and have got to know many of them well.

Javier's an old male that we started seeing about two years ago.

I love the fact that you give wild creatures names like Javier,

for a crocodile.

-He is a beautiful crocodile.

-OK.

So my wife named him. OK, after who?

After the actor. Javier Bardem.

Oh, OK. I'm with you!

Same sort of gnarled looking, beautiful...

Have you named one after a supermodel or anything yet?

I'm waiting!

The couple believe individual crocodiles

have distinct personalities.

But they would never underestimate any of these creatures,

least of all this one.

(Look at the size of that crocodile there!)

Mr T is a particularly aggressive male.

CROCODILE HISSES

-I don't know if you heard him, but he just hissed.

-Yeah.

So he's basically saying, "Look, don't get any closer."

It's like a low level threat and his response.

And if we did get too close to him, he might actually strike out at us.

And the fact that it's staying still means that it's really brazen

and confident.

Usually they're really skittish and they disappear into the water.

Look at those teeth.

Crocodiles bask in the sun

because they can't produce their own body heat like we do.

They need to warm up to be active.

-That was really quick.

-That was like...

That was like a gun, that's like a gun, isn't it?

Look, there's no ripple, nothing. It's just disappeared under.

We move away from this giant's patch

and stop at a spot we think will be safe for my test dive.

So how many dives have you done, Brad?

Probably four, 500.

Four, 500. Andy, are you about the same?

Yeah, about... I would have said about 300.

But that's Brad and I, we always have that issue.

I've done 24.

One of which was in a swimming pool in Chiswick, in West London.

I don't think that actually technically counts.

As lead safety diver, Andy is the one in charge.

'But as the time approaches for me to go into the water,

'I feel more and more vulnerable.'

-And you have a hood?

-I've got a hood, yeah.

OK, are we about ready to go in?

-No, no, no, no, I need my knife!

-Oh, your knife!

-My knife!

Where are you going to put it?

-On my calf, I think.

-Probably the best place.

Next to my right hand, so I can draw it quickly.

Is that really going to actually do anything?

Well, depends what you want doing. I don't know.

'I'm hoping not to meet a crocodile this time.

'But I need to know what to do, just in case.'

We can't say there's not going to be a crocodile, there could well be a crocodile.

In which case, it's going to be the worst of two scenarios, for you.

You'll have the first time big current and the first time croc.

What you have to avoid, Ben, at all costs,

-is drifting onto that crocodile.

-OK.

-OK. That's why you've got a lot of weight on.

-Yeah.

If Brad gives the signal for crocodile,

you have to grab something, you have to grab a branch,

get onto the bottom and stay there, because we are going upstream, drifting with the current.

If there's a croc lying downstream you can't drift onto it or over it.

-That is a very dangerous position to be in.

-OK.

Either the crocodile's going to sit there, you're going to drift onto it and it's going to snap at something

at a leg or... Or you're going to drift over it

and it's going to see you as a silhouette which is, you know, could be a big fish,

it could an animal on the surface floundering, which is what we want to avoid.

'The idea of diving where there might be a crocodile seems crazy.'

Nice and snug under your chin.

The surface is the kill zone where crocodiles attack.

'So I've been instructed to follow Brad and Andy to the bottom

-'as quickly as possible.'

-OK, Ben. Three, two, one. In.

'I've been told it's critical to stay on the river bed.

'If I'm above a crocodile, it will see me as prey.

It's kind of eerie

as your eyes start adjusting to your underwater world.

Shafts of light coming down.

This is beautiful down here.

It's like another world.

'Brad and Andy only dive here during the winter months,

'as crocodiles lose their appetite when the water is colder.

'Visibility is also better at this time of year,

'which means there's less chance

'of bumping into a crocodile unexpectedly.'

'As we swim out to the main channel, the current gets much stronger.

'Beyond anything I've ever experienced.

'I feel totally out of control.'

'As we struggle with conditions, our worse-case scenario happens.'

Oh! Oh, my God!

Oh, that's too close!

There it goes.

Off into the gloom.

'Brad and Andy believe one of the reasons that crocodiles don't attack

'is because they see divers as other crocodiles.

'But this test dive has gone way beyond what I expected,

'and it's time for me to get out of the water.'

I've never jumped out of the water so quickly in my life!

Well, I didn't expect to see a crocodile then.

There's a lot going on.

The current is pushing you, the sediment is cloudy.

-The croc was quite small and flighty.

-Yeah.

-Really young croc.

It disappeared like that and that's even more disconcerting,

cos it's like, "Where is it now?"

The way it glides through the water and then it settled on the sand

and you could see... I could see every colouration on it.

And you could see its eyes just staring forward.

It was beautiful. I never thought I'd say that about a crocodile,

-but it was beautiful.

-Did you feel in any danger around it?

-How did you feel, was it comfortable?

-I didn't feel comfortable, put it that way,

but I felt reassured that these guys were around.

You know, it's the first time I've seen one underwater like that.

'It's very scary under there. But it's beautiful.'

It's confronting your own fears and your own prejudices,

cos I never thought I could even go into an African river,

let alone one teeming with crocodiles.

People in Botswana have no choice

but to use these waters to make a living.

And as the Okavango's crocodile population grows,

attacks will increase.

Nile crocodiles are opportunistic predators.

They'll eat anything from fish to small hippos, wildebeest...

..and people.

'After 15 years of working with crocodiles,

'Adam is well versed in how they attack.'

We've all heard of the death roll. Does this thing exist?

Yes, yes, and it's very well named.

The croc's jaws are designed to clamp the body onto something.

These things are like vices, and then the croc uses its body -

its incredibly powerful, muscular body - then to rip things apart.

And if it's on the surface, it'll flick its head,

but if it's underwater, particularly if it's something large,

they'll spin their body on the axis.

And they can do this two or three times a second.

And you imagine something grabbing onto your leg

and spinning two or three times a second, it's impossible to do anything against that.

Your leg is going to separate from your body.

And what the crocodile will do is he'll grab you

and then he'll take you down.

And so you tend to drown.

So you're usually dead before they start dismembering you.

Everyone in the Okovango Delta knows someone who's been attacked.

'I'm on my way to meet Retsi Sashama and her mother, Mrs Mangwe,

'who know all too well the dangers of living near crocodiles.'

Very nice to meet you, very nice to meet you.

Hello. Hello, madam, hello. How do you do?

What can you say when you see something like that?

When two people's lives, a family, has been turned upside down.

That is a statistic brought to life.

For me, up until now,

it's been the invisible side of the human-crocodile conflict.

It's incredible that Retsi and her mother fought off a crocodile

and lived.

The long-term goal of our underwater research is to learn enough about

crocodile behaviour, so that people know how to avoid being attacked.

Tomorrow, Adam's going to attempt his first ever underwater tests

on wild Nile crocodiles.

If this pilot study is successful,

it could open up a whole new method of researching crocodiles.

Well, what I want to find out is what crocodiles are capable

of perceiving when they're underwater.

I'm hoping that we'll get some insight into that through some of these tests.

'We'll be concentrating on key behaviours.

'Where do they hide before attacking

'and how do they detect prey from underwater?'

-But the question is just how well can they see underwater?

-So ideally,

these balls, we're going to give to Ben to go

and move past the croc?

Oh, yes? I'm already working this out. To see the eye movement,

you'll need to be very close underwater. Closer than we are now!

You've got to remember that these are unpredictable,

but they are also wild animals and dangerous. And you know that.

And we don't want to push too far.

The last thing I want is diver's mud prawning it in every direction

because the croc finally thinks he's going to eat something.

'The dive team head out to a channel filled with hippos,

'known as the Filipo Channel.'

If the research is go to ahead safely and successfully,

Adam must rely on Brad and Andy's experience.

There's no room for error.

This is the first time I have consciously got in the water with...

Certainly with a crocodile that was capable of killing me.

If that guy that went in the water over there is anything to go by,

this crocodile could give me a lot more than a nip if it bit me.

Yeah, go. We'll see you down there.

'The focus of Adam's dive is to test crocodile vision underwater.'

-Ready, so keep the spike away from you.

-OK.

My job is to monitor the safety of the divers from the surface.

OK, Adam. Surface to Mike, Adam is about to come in.

Three, two, one... Adam in water.

Watch the sediment when you get down.

Going to get down pretty bad.

Surface to Adam, do you copy, over?

Surface to Adam. Do you copy, over?

I can see their bubbles, they're crossing.

'Even though I can see where the divers are, I can't hear them

'clearly on the radio.

'It's unnerving not knowing what's going on underwater.'

'I think, let's get that boat...!'

UNCLEAR SPEECH FROM RADIO

Get the boat back.

Surface to divers, yeah, copy that, will move out. Over.

'Something has gone badly wrong.'

'For top wildlife cameraman, Mike Pitts,

'it's been one of the most terrifying experiences

'of his career.' So it attacked you?

Right from behind. It came right behind us.

I had to use the camera. He got the bloody light in his mouth!

-It bit me twice, you see the bite marks on the camera?

-BLEEP.

-Didn't bite you though, did he?

-That was so scary!

-Get this up here.

BLEEP!

I don't know how close he was,

but I could see his ears and his teeth very clearly.

And, oh, just this feeling that goes through you...

If it wasn't for Andy I would have had it. I'm not joking.

You realise that, for the first time,

you're actually in the crocodile's environment.

You're not in your own.

And there was nothing I could do, I just thought, "OK, be calm."

It came right up underneath Adam and Adam didn't see it.

Came up to us, settled right underneath Adam and I just...

I just pushed Adam out the way.

It was 30 centimetres below him, watching him.

I pushed Adam out the way, Mike then saw it,

-put his camera on it and it just snapped.

-Snapped on the camera.

It went like that. It was ridiculous.

We're spending too much time on the surface,

which is enticing them to be predators.

-It didn't look predatory to me, to be honest.

-It looked territorial.

-It looked like he was investigating us. He could've bitten me.

-I mean,

you've all got to get your breath, but is this the end of it?

-This is the first interaction we've had like that.

-Ever. In our lives.

-We've never had anything like that.

-And that's...hence the safety diver.

-I can't watch what's going on behind me, yeah?

-I was actually quite reassured by that,

because my body immediately went into, "OK, safety crocodile mode."

If I move quickly, it's going to bite me.

-And I just let myself drift.

-Turn around...

-He was quite aggressive.

'Adam's convinced the crocodile wasn't attacking.

'He thinks it acted defensively

'when startled by the sudden movement of Mike's camera.'

It's all very well when you see Andy and Brad saying,

"We've never seen that."

-Well, they have now!

-2.7 metres.

What Adam had to his advantage was that he knew to remain

absolutely still. He didn't even talk into his mask.

And I know I wouldn't have done that.

I just know my instinct would have been to start finning away

or to start talking, because I'm a presenter, it's what I do.

I just start talking about my surroundings.

And that's quite scary.

Yeah, I was feeling as confident as you can get,

and that's just thrown me completely,

because it's just the safety brackets around it

have just been stretched.

'Today's incident was a harsh reminder that we're diving

'with a dangerous animal.'

It's also called into question

whether it's safe enough to continue our expedition.

'Everyone's had a night to reflect on what happened.'

None of us want to risk an attack.

But can we be sure that Brad and Andy's protocol for diving

with crocodiles will keep us safe?

Yesterday was a bit of a disastrous day all round in my eyes.

So I'm a little concerned that maybe that trust has been breached.

I don't think anything like that will happen again. If I thought it was likely to reoccur,

we wouldn't be back in the water.

We just need to learn to minimise the time on the surface.

We need to actually streamline our whole process.

I had kind of a slightly restless night's sleep.

Just debating, you know, cos it's not...

Everything yesterday just threw the balance out a little bit.

And it is amazing what a night's sleep can do.

I do feel clear minded and I do completely trust Andy and Brad.

And that's the bottom line, I totally trust them.

I go by human instinct and I will go in today.

It doesn't make me any less nervous.

I'm pooing myself, that's the only way to describe it.

'We're all anxious.

'So Brad suggests we head down the main channel to find

'a female crocodile that he knows called Tutwana.

'She might allow us close enough to study her.'

'We speed up our entry into the water

'to attract less attention at the surface.

'Our aim is to pick up yesterday's research, observing the crocodile's

'visual reactions underwater.

'Adam has asked us to get close-up shots of the crocodile's eyes.

'Within minutes, we find Tutwana.'

I can't believe that just a couple of feet away from me,

is a crocodile. A wild crocodile.

I actually don't feel very comfortable when I've got my head

turned away from it. I'm just going to have another little look.

Look at those teeth!

You can see them from a long way away.

Those powerful, white teeth

that they use for ripping their prey apart.

Their teeth gleam bright white in the gloom.

Crocodiles have a constant razor sharp supply.

Each tooth is replaced every ten months.

I am with it in its natural habitat.

Something that very, very few people ever get to see,

and I am petrified.

I'm totally in Brad's hands here.

'I follow Brad's diving protocol -

'keep calm, stay tight to the bottom to avoid looking like prey

'and keep out of striking range of her jaws.'

I still feel I'm too close.

Cos this looks huge.

It's bigger than me.

And you suddenly realise what power a creature like this must have.

You'd be defenceless.

'Amazingly, there's no sign that this crocodile will attack us.

'Andy and Brad could be right.

'Maybe it does think I'm just a small crocodile and no threat.'

'Ben to surface, it's sitting on the bottom.'

It's very relaxed.

Sitting out of a current.

Its eye looks glazed over.

Ooh, it's just moving, one second.

Oh, my God, this is so close!

BEN GROANS

Just went straight past my head!

Just starting to move.

I'm a bit worried it's going to come down towards us.

I'm sure it's looking at us. It knows we're here.

But I feel certain that it can tell it's being watched.

So Ben just said that he was sure that the crocodile

was looking at them.

And, of course, it's hard to be certain,

but this is one of the questions - how well can they see underwater?

See, a lot of crocodiles live in really murky water,

but this is crystal clear. So why would they not use vision?

And they've got a transparent, nictitating membrane.

There has to be a reason for that.

They have to be able to see shadows and shapes.

And I reckon this croc can see them moving close,

but he probably doesn't quite know what he's looking at.

My heart is pounding away.

It's so near, it makes little movements.

And it just looks like... Oh, here it goes,

it's making a move in front again.

Oh!

Holy crap!

Sorry, that's not very scientific, but that's how you feel.

Crocodiles don't have gills. They breathe air like us.

They can slow their heart rate down to just a few beats an hour,

which helps them to stay underwater for more than 45 minutes at a time.

Just edging closer and closer.

I can see her tail really close.

And her scutes, as they keep describing them,

which is how they identify one crocodile from another.

This has got to be one of the most extraordinary encounters

I have ever had.

Look how close! I feel I could just reach out and touch her.

I could! Oh, it's moving off slowly.

Off into the gloom.

Well that was properly my first crocodile encounter.

I'm actually shaking.

Um...

It's difficult to describe what it's like.

What you have to remember is this is a wild creature in its wild habitat,

and it accepted us here.

It's truly extraordinary.

-Woah, thanks.

-Well done.

OK, that's fine, you can do the other side.

It's incredible.

So close.

Really scary, but magical.

We followed it for about, probably, about 10, 15 minutes, really.

And, uh, amazing.

My heart's still pounding.

Thanks, Brad.

-A lovely little interaction, huh? Lovely little croc.

-Incredible!

You see how amazing, how they sit? When you get really close to them?

They're aware of you, but they don't panic. They're not, you know...

The one bit where it turns and kind of started coming towards me...

But you said that it might do that and I just stayed still,

so it's just about playing by those rules that you've set in place.

I can go so far as to say that was the scariest thing

I've ever had to do. Without question.

I'm really proud that I was able to overcome those fears.

And those fears were partly based on prejudices that I had

about crocodiles. Those fears that are ingrained in all of us,

that crocodiles equal death.

I hope that I'm getting a small insight into

a misunderstood creature.

Adam reviews the day's footage.

Oh, and that... Just beautiful.

This is just remarkable. I can't believe what I'm seeing, actually.

It's offering tantalising clues as to how crocs may achieve

underwater vision.

One of the theories I had was that the nictitating membrane

was basically acting like a contact lens.

The nictitating membrane protects the crocodile's eyes when submerged.

But Adam has never been 100% sure how well they can see through it.

I mean, that eye, that nictitating membrane looks so clear.

Sometimes when you actually see it from a different angle,

it's got an almost pearlescent look to it.

The footage is helpful, but not conclusive.

And Adam wants to know more.

Almost a week into the expedition, and Adam's preparing

to introduce some interactive props to our research.

He's developed his own close vision test.

This is actually a multi-function, data acquisition device.

So there's marks on here at one-foot intervals,

so hopefully I can measure the animal's tail

and get some idea of its total length.

And then this, we're going to be using for the vision test.

So I'll actually pull this off so I can extend this out

and the aim is to actually push this to the side of the crocodile's head

and see whether it responds.

See whether it can see it at a certain distance from the head

and at a specific angle.

This is an important moment for Adam.

His close vision test has never been undertaken on a wild crocodile.

He selects his first test subject and sizes it up.

A croc's length is roughly double its tail,

making this one three metres long.

Next, Adam conducts his vision test,

carefully extending his pole towards the crocodile's eyes

to see at what point it will respond.

The sight test is a success.

But then something happens that none of us had anticipated.

The croc makes off with the equipment,

pulling Adam in its wake.

It behaves more like a dog with a bone than a killer.

Adam lets go and, moments later,

the croc reappears with what looks uncannily like a smile.

It heads for the surface to breathe, clutching its new toy.

Oh, boy!

Yeah?

How was that?

-That was worth the wait!

-Oh, was it?

Well, is it going to react?

What do you reckon the result of that test was?

Definitely a positive result.

-And that's why...

-I've got a shot of him, he's going down the thing

-with a fishing rod. At the end there's this croc pulling him!

-I'm glad you're all laughing!

He's actually got the croc on the end of the stick!

He's swimming around like...

I thought, "If I can just brace myself, then he'll pull it off."

And I did and he eventually pulled it off.

Then he started swimming along with this polystyrene ball in his mouth.

-See what he did immediately?

-Straight to the surface.

-Straight to the surface, so he can crunch it and swallow it.

-Yeah.

-They have to surface to do it and he went straight up.

-What that showed me, quite clearly,

there's absolutely no doubt that the crocodile can see underwater.

I deliberately moved the ball gradually into its field of vision.

And it didn't respond at all,

until it got to directly perpendicular with the head.

At that 90 degree angle, suddenly the crocodile's head moved.

So yeah, I'm in absolutely no doubt about it at all.

That crocodile, at a distance of

probably about 80 centimetres,

could detect that white object in the water.

There it is, right at the end of the channel.

Adam retrieves the ball gingerly,

'in case the crocodile is still close by.' Well retrieved.

There you go. Remarkably little... Remarkably few bites in that.

So as she tried to crush it, she bit it and then spat it out, basically.

We're beginning to build up a fascinating picture

of how crocodiles sight their prey.

But not everybody shares our enthusiasm for these

incredible animals.

'Given the number of attacks in the delta,

'it's hardly surprising that most locals here

'see crocs as a deadly threat that they'd rather be rid of.

'The fact that they're a protected species is something many locals

'are at a loss to understand.'

-Vince, hey there.

-How're you doing?

-How are you? Good to see you.

-Are you well?

-Very well, very well.

-Thanks for this.

-No worries at all.

Our ecologist, Vince Shacks, is keen to teach that crocodiles here

are protected for a very good reason.

OK, good morning, everybody.

-ALL:

-Good morning.

Today we're here to talk to you about crocodiles.

How many of you have seen a crocodile in the river before?

That's everybody has seen crocodiles.

The river here is very healthy.

We've got lots of fish, we've got clean water,

we've got lots of crocodiles, we've got lots of bream.

So everything is working very, very well,

because every one of the food chain is there today.

'The crocodile is a key predator in the Okavango Delta.

'Its main source of food is the catfish, or barbel

'which, in turn, eats the smaller bream -

'an important fish for the local people.'

So if take the crocodile out...

Less crocodiles mean more barbels.

So if there's more barbel, there's less bream,

so now the bream are going to disappear.

All the fish that we like to eat, that taste very nice,

are now going to disappear.

OK.

Very nicely.

And a lot of these kids will have grown up, probably

-being told by their families...

-Absolutely.

..warned about crocodiles. Probably seeing them as a pest.

Yes. No, no, definitely. Almost certainly, you know?

So we want to get that message across that there's

a little bit more to them.

But the hard truth is, at some point in their lives,

most of these children will know someone who's been attacked

by a crocodile.

What do you think?

Rough. Rough here.

But have you felt underneath? Try feeling the belly. Woah!

It is a bit confusing, in my mind, where you draw the line

between conservation, protection, understanding.

But the more I spent time here, the more I feel convinced

that the more we understand about the crocodile,

the better we can have that harmony.

Back at base, Adam reviews today's footage.

He's increasingly curious about where crocodiles choose

-to lie in wait.

-Sometimes, they'll strike.

-They've sort of got a bolthole.

-Yeah.

They'll move from the basking site a little bit up or down.

It's almost like a cave, underneath, that's cut out under the bank,

isn't it?

Adam really wants to find out why a crocodile chooses a certain patch.

Is it to do with the water temperature?

Is it to do with the strength of the current,

is it to do with the sunlight coming through?

The crocs that we see regularly, go to the same places.

To me, that's a really interesting question. What is it about

these places that these crocodiles are finding comfortable?

Why are they moving there?

Understanding where and why they hide will give us

a better idea of where they might attack.

I can write underwater with this thing.

I'm going to take some temperature measurements around the crocodile

and I'm also going to actually try and get a light meter recording

where the crocodile's resting.

Over the next few days,

Adam and I submerge into his underwater laboratory.

We're testing both the main river channel

and caves under the bank to see which spots crocodiles prefer.

If you could get a water temperature reading on the croc

and just let me know over comms and I'll just write it down here.

-That'll be great.

-OK.

-Just clip it on somewhere that'll be easy to see.

-Yep.

Go.

We take measurements of current speed,

light levels and water temperature.

This way we can establish their ideal environment.

It appears crocodiles prefer sheltered caves

which are warmer than the open water.

We also discover that crocodiles are less likely to be found in areas

with strong currents -

vital information to those living on the river.

If you're looking at it from the perspective of someone

who was coming down to the water, if there was a really flat,

fast-flowing, deep channel directly beneath you,

there would actually be a lot less chance of there being a crocodile

down there, compared to a much more open channel where the flow rate is a lot less.

Winter here is coming to an end.

As the water warms up, crocodiles will become more interested

in feeding, making it too dangerous to dive.

'So today is our last chance to work with these crocodiles this year.'

Last day.

Strange. It's amazing how, if I think back to those first few days,

you know, it was so terrifying.

And now, I'm actually quite sad that this is my last dive.

I'd love to go out with one final, amazing encounter.

And all my fingers.

So far on this expedition we've achieved most of what

we set out to do.

We had one close call,

but we've also made some groundbreaking discoveries.

We have one last aim -

to find out whether the larger and more dominant crocodiles

in the area, will tolerate our presence in their lairs.

We go in search of a giant crocodile that Brad calls Mawasi -

a Botswanan word for "scaled creature."

It doesn't take long to find him in his lair.

It knows we're here.

But it's putting up with us.

The reality is, this could kill me instantaneously.

And it's terrifying for that.

This is the biggest crocodile I've ever seen.

I estimate it's probably four metres.

'This huge crocodile has been defending its territory

'its whole adult life,

'yet doesn't react to me at all.'

I mean, a big three-and-a-half, four metre crocodile is way overkill

in terms of being able to kill you.

Definitely. They're capable of dealing with large mammals

and, I mean, we're just a snack.

Ah, there it goes.

'It moves so effortlessly, so beautifully.

'Since I've been here,

'I've discovered that crocodiles walk underwater, rather than swim -

'a clever and most graceful way to conserve energy.'

I'm really beginning to see a different side of crocodiles now.

Terror is turning into a sort of fascination.

I'm still scared...

..cos this is a wild creature.

I'm actually quite jealous right now.

I would love to be down there right now...

actually seeing this crocodile, as well.

But I think this is pretty much establishing that you can get

in the water with these crocodiles, and as long as the circumstances

are right, the crocodile's just not bothered.

I'll never quite look at crocodiles the same way again.

Still looking forward to getting back into that boat, though!

Absolutely huge!

It'll be interesting to hear what Brad's estimation was.

Probably four metres. Maybe I'm doing a typical male thing,

saying it was bigger than it was, but honestly, I was like this...

to its tail. Just there.

Did you resist the temptation?

-I got close enough.

-I'm very glad that...

-Thank you. And I'm so...

-..I've changed your perceptions.

..proud to have been part of all of this. Thank you, that was... How big do you think that was?

-I said four metres.

-It's definitely over three.

-Over three.

-Definitely over three metres.

-Probably nearly four!

'Our pilot study has been a success and has opened the door

'to a revolutionary new way of researching wild crocodiles

'in the future.

'We've shown they can be studied underwater.

'And we now have a better understanding of their vision

'and where they hide.

'We've found that, underwater, crocodiles avoid

'fast-flowing currents, so those areas are safer for local people.

'We've also learned that if you do encounter a crocodile in the water

'and can't get away,

'diving to the bottom might be the safest thing to do.'

As a scientist, the most exciting thing, for me,

is the fact that there's a new opportunity to collect data in a way

that's never been done before.

We can start to really ask questions that haven't been asked before.

If this is how crocodiles are behaving underwater,

how can we modify our behaviour,

so that we can make it safer for people who live around crocodiles?

It's been an incredible journey.

You know, I've seen so much, I've learned so much along the way.

I've obviously seen the sharp end of crocodiles,

I've seen that they can be killing machines and the effect

that they have on people who have to live alongside them.

Thank you so much. It's been...

'But I've also seen that they're misunderstood creatures.

'And maybe some of this research might change that relationship

'between crocodile and man.'

It's been amazing! Really, really amazing.

-Oz next.

-Australia next.

-We'll see you in Australia in a few weeks.

Well, he survived.

Good thing, too!

'Next time, we face a very different underwater challenge...

'Australia's salt water crocodile.

'The largest...'

Her back leg, sorry.

'..and most aggressive reptile on earth.'

Back, back, back, back, back!

This is crazy!

'No scientist has ever dived with a wild saltwater crocodile before.'

Why is he opening his mouth now and looking at me?

Is he about to launch up?

Quite frankly, it's a terrifying prospect at this moment.

Subtitles by Red Bee Media Ltd