0:00:03 > 0:00:07An expedition is exploring one of the last frontiers on Earth.
0:00:09 > 0:00:13Penetrating the depths of the Amazon River,
0:00:13 > 0:00:17they've already found some extraordinary creatures.
0:00:19 > 0:00:22Knifefish that communicate with electricity.
0:00:24 > 0:00:28Blind freshwater dolphins.
0:00:28 > 0:00:32And they've discovered a new species of blood-sucking catfish,
0:00:32 > 0:00:35never seen by scientists before.
0:00:35 > 0:00:38This is perfect. This is ecotheological history.
0:00:39 > 0:00:45But heading upstream into the deepest jungle, they hit a problem.
0:00:45 > 0:00:47CRASHING
0:00:47 > 0:00:49Their boat struck ground.
0:00:49 > 0:00:52That's not good. It sounded to me like either a shaft is bent
0:00:52 > 0:00:54or there's struts flapping around.
0:00:54 > 0:00:57The thing is, we're taking on water through the stern.
0:00:59 > 0:01:02The whole expedition is on the rocks.
0:01:15 > 0:01:20The team's lead boat has limped back to port.
0:01:20 > 0:01:23It's not easy to find spares in the Amazon
0:01:23 > 0:01:26and it's taken two days to repair the hull and propeller.
0:01:28 > 0:01:31Now they're behind schedule.
0:01:38 > 0:01:40In this phase of the expedition,
0:01:40 > 0:01:45the team's task is to explore the deepest parts of the Amazon.
0:01:45 > 0:01:51Hidden under the water, there are some deep channels gouged into the river bed.
0:01:51 > 0:01:55Scientists have no idea what lies in their depths.
0:01:58 > 0:02:03But to dive them, first they have to find them.
0:02:04 > 0:02:08I feel very comfortable that we are going to see something we have not seen before.
0:02:08 > 0:02:11I really, strongly feel that.
0:02:11 > 0:02:13We're going far deeper than we've been before.
0:02:13 > 0:02:16I'm really excited about what we're doing right now.
0:02:26 > 0:02:28A trench has been located.
0:02:28 > 0:02:30There are deeper ones,
0:02:30 > 0:02:34but this is still big enough to hide the Statue of Liberty.
0:02:34 > 0:02:36No-one has ever been to the bottom.
0:02:39 > 0:02:42The currents here are fast and unpredictable.
0:02:42 > 0:02:45It will take good seamanship to secure the boat safely.
0:02:55 > 0:02:59The divers must compose their minds before they enter the water.
0:03:06 > 0:03:09For Mike and his dive partner Florian Graner,
0:03:09 > 0:03:13it will be all too easy to get lost or swept away by the current.
0:03:16 > 0:03:21They will be diving deeper into the Amazon than anyone has ever been.
0:03:50 > 0:03:53The river is a soup of stirred-up sediment.
0:03:53 > 0:03:55The deeper they drop,
0:03:55 > 0:03:56the worse it gets.
0:04:15 > 0:04:22The surface crew monitor every word and a safety diver waits on standby.
0:04:22 > 0:04:25Visibility's so bad that he's having to hold on to Florian.
0:04:33 > 0:04:39At the bottom of the hole, the divers sink to their waists in thick, clinging mud.
0:04:51 > 0:04:56They decide to abort the dive and send a surface marker to guide them up.
0:05:01 > 0:05:04They have the most advanced camera in the world...
0:05:04 > 0:05:06but all they have filmed...
0:05:06 > 0:05:08is mud.
0:05:08 > 0:05:14Once you hit the bottom, you can hardly feel hitting the bottom, then, whooom, this cloud came up.
0:05:14 > 0:05:18It is complete blackness, mud, not...I mean the particles...
0:05:18 > 0:05:21that's why I said, "Let's see what this is."
0:05:21 > 0:05:25It was big particles of gunk, just...
0:05:29 > 0:05:33No-one had expected visibility to be this bad.
0:05:33 > 0:05:38There's going to be no way to film deep water creatures in this stretch of the river.
0:05:41 > 0:05:44For now, there's a change of plan.
0:05:44 > 0:05:49They travel upstream in search of water that's shallower and clearer.
0:05:49 > 0:05:53And that means venturing into the very heart of the rainforest.
0:05:53 > 0:05:56We get into the kind of Amazon of the imagination.
0:05:56 > 0:06:00The great dripping forest, maybe a narrower river.
0:06:00 > 0:06:02This idea of going up into
0:06:02 > 0:06:06what we all affectionately call the Heart of Darkness
0:06:06 > 0:06:10is something that I've been looking forward to for the entire trip.
0:06:13 > 0:06:17There's a labyrinth of lakes and forest streams
0:06:17 > 0:06:18that feed the main river.
0:06:22 > 0:06:23In the Amazon,
0:06:23 > 0:06:28the strangest creatures swim through the trees of the deepest jungle.
0:06:42 > 0:06:47The next afternoon, the expedition is surrounded by virgin forest.
0:06:52 > 0:06:54They decide to split into two teams.
0:06:54 > 0:06:58Cameraman Mike de Gruy and naturalist Kate Humble
0:06:58 > 0:07:01will be looking for clear-water jungle streams.
0:07:01 > 0:07:04Hasta la vista. Let's go.
0:07:04 > 0:07:07Our plan is to go up river about an hour
0:07:07 > 0:07:11and find another little stream which comes out and explore another lake
0:07:11 > 0:07:15which has different fish, including, we hope, electric eels.
0:07:18 > 0:07:22Of the thousands of species that live in the jungle waters,
0:07:22 > 0:07:25the electric eel is king.
0:07:25 > 0:07:29They hunt with 600-volt electric shocks
0:07:29 > 0:07:33and use the same weapon for defence.
0:07:33 > 0:07:35This fish breathes air.
0:07:35 > 0:07:39Uniquely adapted to the oxygen-poor waters of the Amazon,
0:07:39 > 0:07:41the lining of their mouth acts as a lung.
0:07:46 > 0:07:49I need a pick-me-up before I go out there.
0:07:49 > 0:07:53Second team leader Mike Pitts sets himself up for the day.
0:07:53 > 0:07:55Brazilian coffee.
0:07:55 > 0:08:00He's going to a jungle lake to film rare fish.
0:08:00 > 0:08:04But it's also rumoured to have a large crocodile - a caiman.
0:08:04 > 0:08:06One with a grudge against people.
0:08:06 > 0:08:08Somebody shot at it
0:08:08 > 0:08:13and it's got either an eye missing or it's got a crease above its eye.
0:08:13 > 0:08:16It's been hit by one of the fisherman or locals,
0:08:16 > 0:08:17they were worried about it,
0:08:17 > 0:08:19which I think is a bit unfair.
0:08:19 > 0:08:21Do you think that will make it more nervous?
0:08:21 > 0:08:23It might have an attitude.
0:08:23 > 0:08:25It might have an attitude problem!
0:08:25 > 0:08:27Are you going to accompany us on this one, mate?
0:08:27 > 0:08:29No, thanks, I've got work to do!
0:08:29 > 0:08:31He's more sensible than that!
0:08:34 > 0:08:39Nearby, Mike and Kate are looking for a stream with clear water.
0:08:42 > 0:08:44Well, we wanted overhanging forest, didn't we?
0:08:44 > 0:08:46Yeah.
0:08:49 > 0:08:51We can go in and snorkel first.
0:08:51 > 0:08:54- OK, well, why don't you get in? - See what it looks like.
0:09:04 > 0:09:08Mike finds a world of tangled roots and poor visibility.
0:09:20 > 0:09:23These are a lot of the same fish that we saw.
0:09:23 > 0:09:25Yeah.
0:09:25 > 0:09:28I'm going to go and look in the trees.
0:09:29 > 0:09:34Every stream and river is different and they never know what to expect.
0:09:34 > 0:09:35How is it?
0:09:40 > 0:09:42Very muddy.
0:09:42 > 0:09:44I don't see anything that we haven't seen before.
0:09:44 > 0:09:47They'll have to try somewhere else.
0:09:50 > 0:09:53Mike Pitt's team carry their equipment through the jungle
0:09:53 > 0:09:56to the lake with the one-eyed caiman.
0:10:02 > 0:10:06There are two local guides on the expedition,
0:10:06 > 0:10:10Eduardo Gomes and Samuel Basilio.
0:10:10 > 0:10:14They believe the lake is their best chance to find unusual fish.
0:10:14 > 0:10:16My pants have fallen down!
0:10:16 > 0:10:19We checked before, me and Eduardo,
0:10:19 > 0:10:21and there is a big caiman over there.
0:10:21 > 0:10:24I just heard another story about a snake here -
0:10:24 > 0:10:27the anaconda - but you never know.
0:10:27 > 0:10:29There are a lot of stories about it.
0:10:29 > 0:10:32We just want to be sure that nothing can happen to our divers.
0:10:32 > 0:10:36Three days ago the guide saw some of them at the end of the lake.
0:10:36 > 0:10:38- The anaconda?- The anaconda.
0:10:38 > 0:10:43It wasn't that big. About six metres - about 18 feet long.
0:10:43 > 0:10:45- So...- Big enough for me.- Yeah.
0:10:45 > 0:10:50The team's filming permit doesn't allow them to carry a rifle.
0:10:50 > 0:10:52They have to rely on Eduardo's bow and arrow
0:10:52 > 0:10:54in case the caiman strikes.
0:10:57 > 0:11:01On their way back to the boats, Mike and Kate take a short cut -
0:11:01 > 0:11:02or so they think.
0:11:04 > 0:11:08Fallen trees are a common obstacle for locals
0:11:08 > 0:11:11but for strangers it's a bit of a puzzle.
0:11:11 > 0:11:13Kate, I gave you a Swiss army knife.
0:11:13 > 0:11:17If you've brought it, could you please cut that log out of the way?
0:11:17 > 0:11:19Well, let's think.
0:11:19 > 0:11:21Is there any way round this?
0:11:21 > 0:11:24- We could lift that over. - Yeah, we'll have to...
0:11:24 > 0:11:29What about if we can pass people over the tree and into the boat?
0:11:33 > 0:11:36Mike, help! What's going on?
0:11:38 > 0:11:40You want to lay it down?
0:11:40 > 0:11:43It won't leak? How do you say leak?
0:11:43 > 0:11:47I just don't want gasoline in my boat. We're going to go over.
0:11:47 > 0:11:48Here.
0:11:50 > 0:11:54I see what's he's saying. I like his idea. It's going in the water.
0:11:56 > 0:12:00I think that is a great idea.
0:12:01 > 0:12:02You got it?
0:12:02 > 0:12:06- There's more than one way to skin a cat.- I've got it!
0:12:08 > 0:12:10Come on! Just make a decision!
0:12:10 > 0:12:14I got it! I got it. There we go.
0:12:19 > 0:12:21There, that was easy!
0:12:27 > 0:12:29Mike Pitts' team enter the lake
0:12:29 > 0:12:32rumoured to have the one-eyed caiman.
0:12:35 > 0:12:37It's a big lake.
0:12:37 > 0:12:40Yeah, there's a lot of places for the alligator to hide.
0:12:45 > 0:12:50Eduardo makes baby caiman distress calls.
0:12:50 > 0:12:53If adults are here, they'll show themselves.
0:12:53 > 0:12:57I'm sure you guys are right. There's gonna be stuff in here.
0:13:00 > 0:13:05Local children gather to watch the oddly dressed strangers.
0:13:07 > 0:13:09The circus has come to the jungle.
0:13:11 > 0:13:14Yeah, we got it. I got it, I got it.
0:13:26 > 0:13:31A school of angelfish drift by in this underwater jungle.
0:13:36 > 0:13:41Most tropical fish kept in captivity come from the Amazon.
0:13:45 > 0:13:48Everybody watching them and the little boys are saying
0:13:48 > 0:13:52they don't know how these divers can swim with their big shoes
0:13:52 > 0:13:55and they can't believe they can swim so fast
0:13:55 > 0:13:57and go under the trees like that.
0:13:57 > 0:13:59It's a big entertainment for them.
0:14:03 > 0:14:07Meanwhile, the edge of the lake is being searched
0:14:07 > 0:14:10by diver and cameraman Florian Graner.
0:14:10 > 0:14:14Well, here we have a whole group of little caimans.
0:14:14 > 0:14:17He must approach very slowly.
0:14:17 > 0:14:22If these babies make an alarm call, the parents may come.
0:14:22 > 0:14:26We are wondering where the mum and dad are, really.
0:14:26 > 0:14:29(Where's Mama?)
0:14:29 > 0:14:32(Where's the adults?)
0:14:41 > 0:14:44There's still no sign of Mother.
0:14:44 > 0:14:48And the babies are getting very relaxed.
0:15:13 > 0:15:15They're becoming quite sociable.
0:15:17 > 0:15:20- What's he doing? - HE LAUGHS
0:15:20 > 0:15:23That's just unbelievable!
0:15:23 > 0:15:27Those caimans have just come up right to the camera and to me!
0:15:27 > 0:15:32I didn't have to go to them, for a change!
0:15:39 > 0:15:41In the middle of the lake,
0:15:41 > 0:15:45Mike Pitts finds a school of silvery Amazon brycons.
0:15:45 > 0:15:50They glide past searching for fruit fallen from the trees overhead.
0:15:52 > 0:15:55Many fish here have developed unique behaviour.
0:15:55 > 0:15:58Mike discovers something remarkable.
0:15:58 > 0:16:02Two cichlid parents are protecting their fry from all comers,
0:16:02 > 0:16:05including cameramen.
0:16:11 > 0:16:15They've dug a deep hole in the sand with their mouths
0:16:15 > 0:16:18to make an underwater nursery for their babies.
0:16:24 > 0:16:26Beautiful fish! Beautiful.
0:16:26 > 0:16:31At night it will be a whole totally different game I think
0:16:31 > 0:16:33because once that sun drops down
0:16:33 > 0:16:37I'm sure it's going to change a lot.
0:16:37 > 0:16:39So I think we should be here.
0:16:39 > 0:16:42I just talked to these guys here. They said be careful
0:16:42 > 0:16:49because at night everything comes out and there are caiman and snakes.
0:16:50 > 0:16:54But it's not only caiman that come out at night.
0:16:57 > 0:16:59The boats have beached for the evening.
0:16:59 > 0:17:04And as the crew relax, all around them is the distinctive sound
0:17:04 > 0:17:06of hundreds and hundreds of bats.
0:17:08 > 0:17:11There's over 100 species in the Amazon,
0:17:11 > 0:17:14including the infamous vampire bat.
0:17:15 > 0:17:19They roost in hollow jungle trees.
0:17:19 > 0:17:23By night they fly the forest feeding on monkeys and other mammals.
0:17:25 > 0:17:29To find out if there are vampires around,
0:17:29 > 0:17:33Kate puts up one of the expedition's nets in the jungle.
0:17:35 > 0:17:39I'm just setting up this very, very fine net -
0:17:39 > 0:17:41a mist net -
0:17:41 > 0:17:47which will trap any bat flying in this direction.
0:17:47 > 0:17:51This will allow us to actually get a good look at one
0:17:51 > 0:17:52without it being harmed.
0:17:52 > 0:17:59Right, I think that's ready. Let's turn the lights off and wait.
0:18:00 > 0:18:03Mike Pitts' team are ready to dive.
0:18:03 > 0:18:08They're hoping the night will reveal fish that can't be seen by day.
0:18:08 > 0:18:14Samuel and Eduardo keep an eye out for the one-eyed caiman.
0:18:14 > 0:18:16If we see caiman coming our way,
0:18:16 > 0:18:22I suppose we all cross our legs, hope for the best and keep filming.
0:18:23 > 0:18:26I think we'll get some stuff so let's go for it.
0:18:36 > 0:18:41In this tangled watery forest, the divers risk getting stuck.
0:18:41 > 0:18:43And every log could hide the caiman.
0:18:45 > 0:18:49But it's worth the risk as they capture behaviour never seen before.
0:18:49 > 0:18:52A transparent sandknife fish
0:18:52 > 0:18:56burrowing through the sediment to escape predators.
0:18:56 > 0:19:01And a striped gar propels itself with the tiniest fin movements.
0:19:16 > 0:19:20Suddenly Samuel confronts something in the water.
0:19:22 > 0:19:26It's a caiman, but certainly not the giant they were worried about.
0:19:26 > 0:19:27This is a red caiman.
0:19:27 > 0:19:31They don't grow big - one and a half metres maximum -
0:19:31 > 0:19:34but it's one of the species that are very deep in the forest
0:19:34 > 0:19:36and it's very aggressive.
0:19:36 > 0:19:37See?
0:19:40 > 0:19:43If you put it here, it will jump on your leg and bite!
0:19:43 > 0:19:46CAIMAN SNARLS
0:19:47 > 0:19:49While Samuel releases the red caiman,
0:19:49 > 0:19:52the team steal an opportunity to film it.
0:20:07 > 0:20:11We've been waiting about 20 minutes...
0:20:11 > 0:20:14to see if there is anything.
0:20:15 > 0:20:19Back in the jungle, Kate checks her bat trap.
0:20:21 > 0:20:23OK.
0:20:24 > 0:20:25What's that?
0:20:25 > 0:20:27Ah-ha!
0:20:27 > 0:20:28Look at this.
0:20:30 > 0:20:35OK, now this is unmistakably...
0:20:36 > 0:20:38..a vampire bat.
0:20:38 > 0:20:43Isn't it funny that a creature as small as this
0:20:43 > 0:20:46should inspire so much fear?
0:20:46 > 0:20:51Pointed ears and this sort of double nose.
0:20:53 > 0:20:55Very elongated canine teeth.
0:20:57 > 0:20:58That's what does the damage.
0:21:00 > 0:21:02Right, I think we should let him go
0:21:02 > 0:21:07and hope to heavens he doesn't double back and bite me for revenge.
0:21:07 > 0:21:09Off he goes.
0:21:19 > 0:21:24Next morning, as they head up river, they find a huge caiman
0:21:24 > 0:21:26with just one eye.
0:21:26 > 0:21:29It wasn't a rumour after all.
0:21:29 > 0:21:32It had moved out of the lake and into the main river.
0:21:32 > 0:21:36Perhaps it was more afraid of the divers than they were of it.
0:21:42 > 0:21:46They've filmed a wide variety of fish in remote jungle lakes
0:21:46 > 0:21:49but there's one creature they haven't seen -
0:21:49 > 0:21:51an electric eel.
0:21:51 > 0:21:57The expedition decide to fan out to find eel streams deep in the forest.
0:21:57 > 0:21:59Let's go!
0:22:06 > 0:22:10Mike Pitts' team will be searching an isolated jungle stream.
0:22:10 > 0:22:12With no boat access,
0:22:12 > 0:22:16they're forced to carry their dive gear through the sweltering forest.
0:22:25 > 0:22:29Kate and Samuel take the chance to search the surrounding jungle.
0:22:34 > 0:22:39There's something about a tree this size
0:22:39 > 0:22:42that kind of renders me speechless.
0:22:42 > 0:22:46- Yeah.- It makes me feel very, very small and very insignificant.
0:22:46 > 0:22:48Now look at this, Samuel!
0:22:50 > 0:22:52That's extraordinary!
0:22:53 > 0:22:55That's the most enormous ant!
0:22:55 > 0:22:58Be careful, that's very poisonous.
0:22:58 > 0:23:02- Now what would these ants normally prey on?- The other insects.
0:23:02 > 0:23:03Other insects.
0:23:04 > 0:23:07Now you can feel - the smell.
0:23:07 > 0:23:11- Oh, yes, it's a really strong acidy smell.- Acid.
0:23:14 > 0:23:18When it stings, it's painful for about 12 hours.
0:23:18 > 0:23:21If you're allergic, it's able to kill you.
0:23:21 > 0:23:23So it can be like a wasp sting.
0:23:23 > 0:23:25- Er, stronger.- Like a scorpion?
0:23:25 > 0:23:27Six or ten times - like a scorpion.
0:23:27 > 0:23:30It's looking for something to bite and sting.
0:23:34 > 0:23:37But electric eels do more than sting.
0:23:37 > 0:23:39One zap can knock a diver unconscious.
0:23:39 > 0:23:42I've been told you're down there
0:23:42 > 0:23:45with a hand grenade with a pin pulled out
0:23:45 > 0:23:49and just thinking, "That's gonna go off any second if I get too close."
0:23:49 > 0:23:52I've been told that if you get closer than a metre,
0:23:52 > 0:23:57it may well give you a really severe shock and it's gonna hurt.
0:24:15 > 0:24:18Despite reports that this stream contains eels,
0:24:18 > 0:24:20they're having trouble finding them.
0:24:33 > 0:24:36Mike is confronted by an angry pike cichlid
0:24:36 > 0:24:39defending its adolescent young below.
0:24:40 > 0:24:44Pike cichlids are a bit like humans in their parenting skills,
0:24:44 > 0:24:48staying together to protect and even feed their family
0:24:48 > 0:24:50until they're nearly fully grown.
0:24:54 > 0:24:58They have the longest parental care of any fish in the world.
0:25:05 > 0:25:09We've had a look in this pool and there's no sign of any eels at all
0:25:09 > 0:25:12and unfortunately we've lost the light.
0:25:13 > 0:25:15But we'll come back. We'll come back.
0:25:15 > 0:25:18But it's a marvellous location, it really is.
0:25:18 > 0:25:20We could spend a week here, couldn't we?
0:25:29 > 0:25:33It's full of spiders, scorpions.
0:25:33 > 0:25:35There is also a lot of snakes.
0:25:35 > 0:25:41The rainforest is full of animals that protect themselves with poisons...even caterpillars.
0:25:41 > 0:25:43Very strong, don't touch it...
0:25:43 > 0:25:46It burn and hurt a lot.
0:25:46 > 0:25:48It hurt for like two to three hours.
0:25:48 > 0:25:50It looks toxic.
0:25:50 > 0:25:53Incredible piece of design though, isn't it?
0:25:55 > 0:25:58They press further into the forest.
0:25:58 > 0:26:01And in a hole in the ground, a creature lurks.
0:26:02 > 0:26:05Very, very different kind of spiders...
0:26:05 > 0:26:08here it comes.
0:26:08 > 0:26:10Oh!
0:26:10 > 0:26:13The giant white-kneed tarantula.
0:26:13 > 0:26:18So this spider would be trapping what?
0:26:18 > 0:26:24Small mammals, birds, insects.
0:26:24 > 0:26:30- Is it poisonous?- Yes. - By using a noose made from grass, Samuel can lasso the spider.
0:26:30 > 0:26:32He must take care.
0:26:32 > 0:26:34This tarantula defends itself
0:26:34 > 0:26:38by flicking stinging hairs through the air at any potential foe.
0:26:38 > 0:26:41Incredible jaws.
0:26:43 > 0:26:45- Isn't that amazing?- It is.
0:26:48 > 0:26:50I've never seen this kind before.
0:26:50 > 0:26:54In the Amazon, new animals are waiting to be discovered all the time.
0:27:06 > 0:27:09Taking the whole forest down!
0:27:09 > 0:27:13- What is this?- Well, this is the water vine. I'm just thirsty.
0:27:13 > 0:27:15We've walked for miles and miles
0:27:15 > 0:27:19and this is really good water. Drinkable water.
0:27:24 > 0:27:26Here.
0:27:35 > 0:27:40That is amazing water though. You could bottle that and sell it for...
0:27:43 > 0:27:44£3 a bottle.
0:27:45 > 0:27:48Oh, this is not a good one.
0:27:51 > 0:27:54I thought it was fine! What's wrong with it?
0:27:54 > 0:27:56Did you want it to taste like beer?
0:27:57 > 0:28:00Isn't that extraordinary though?
0:28:16 > 0:28:21Next morning, the whole team join forces for one last big push
0:28:21 > 0:28:24to try and find the elusive electric eels.
0:28:35 > 0:28:40They think this overgrown stream is their best bet.
0:28:40 > 0:28:41This looks great.
0:28:43 > 0:28:47Obviously these are one of the kings of the Amazon River
0:28:47 > 0:28:53and they can kick out a 600-volt wallop when they're threatened
0:28:53 > 0:28:56or when they want to kill something to eat.
0:28:56 > 0:29:00Anybody comes along they don't want around - kapow!
0:29:00 > 0:29:01And that pretty much does it.
0:29:01 > 0:29:05But before they can get started, the heavens open.
0:29:05 > 0:29:11THUNDER RUMBLES
0:29:12 > 0:29:15The rainy season is due to start any day now.
0:29:25 > 0:29:28If the rain continues, it will muddy the water,
0:29:28 > 0:29:32and it will be impossible to find anything in the river.
0:29:32 > 0:29:35Can you look after my nice dry towel? Thank you.
0:29:39 > 0:29:42But as quickly as the rain started, it stops.
0:29:51 > 0:29:55Kate gets into position to try to spot an eel.
0:29:57 > 0:30:02They need to come to the surface to breathe every 15 minutes.
0:30:04 > 0:30:09Eduardo tries to attract one by mimicking a fish in distress.
0:30:09 > 0:30:13What's that? There's the eel! Just there! There's the eel! There he is!
0:30:13 > 0:30:15He's just there! Everybody stay still!
0:30:15 > 0:30:17The eel's on the move.
0:30:17 > 0:30:19- Eels!- Bloody hell. Just get the...
0:30:19 > 0:30:21- Mike!- ..camera on!
0:30:43 > 0:30:46At first it seems they've missed their chance.
0:30:49 > 0:30:51The eel's disappeared.
0:30:55 > 0:31:00Everybody watches for the moment when the eel must come up for air.
0:31:34 > 0:31:39Finally, they begin to capture an electric eel on camera.
0:31:44 > 0:31:47The divers edge closer and closer.
0:31:50 > 0:31:54If they move too suddenly, they risk being electrocuted.
0:32:08 > 0:32:11The divers are now just inches away.
0:32:11 > 0:32:14Yet the eel tolerates their presence.
0:32:20 > 0:32:23Two? Yahoo!
0:32:23 > 0:32:25That's good!
0:32:25 > 0:32:28It's the most amazing thing. You see it rippling along there
0:32:28 > 0:32:32and all the time I'm waiting for that 600 volts to go through me!
0:32:32 > 0:32:36And could you hear anything? Could you hear any sort of clicking or...?
0:32:36 > 0:32:38No, I couldn't hear a thing.
0:32:38 > 0:32:40I am partially waterlogged in my left ear
0:32:40 > 0:32:42but I couldn't hear a thing.
0:32:42 > 0:32:44That was really good.
0:32:44 > 0:32:49They got very close. That was really dangerous. Very close.
0:33:06 > 0:33:09THUNDER RUMBLES
0:33:09 > 0:33:13It's the final week of the expedition.
0:33:13 > 0:33:17The first thunder storms of the rainy season have arrived.
0:33:22 > 0:33:25But there's one more task.
0:33:27 > 0:33:32The expedition is now heading towards its ultimate challenge.
0:33:32 > 0:33:34Legend has it that in the centre of the Amazon,
0:33:34 > 0:33:38there's an underwater trench more than 90 metres deep.
0:33:38 > 0:33:42I'm entering this with a slight amount of trepidation.
0:33:43 > 0:33:47No-one knows what creatures live there.
0:33:47 > 0:33:50You can't help but to go into it... carefully!
0:33:53 > 0:33:56Their aim is to take cameras into this chasm
0:33:56 > 0:33:58to search for signs of life.
0:33:58 > 0:34:02They'll be the first people ever to explore the Abyss.
0:34:02 > 0:34:04Now, one thousand miles from the sea,
0:34:04 > 0:34:08they are nearing the deepest point of the Amazon.
0:34:11 > 0:34:15To help them film at these punishing depths,
0:34:15 > 0:34:19the expedition has just taken delivery of a very special piece of kit.
0:34:19 > 0:34:25- Yes!- For Mike, it means they have a real chance of success.
0:34:27 > 0:34:28- Fantastic.- You're kidding.
0:34:28 > 0:34:31Look at this!
0:34:31 > 0:34:35This is an ROV - a remotely operated vehicle.
0:34:35 > 0:34:39With it, they hope to make scientific history.
0:34:39 > 0:34:42This goes way deeper than any of us can go.
0:34:42 > 0:34:45We can take this, place it in a spot,
0:34:45 > 0:34:50it can stay down 24 hours a day as an eye in the river.
0:34:50 > 0:34:57We've got cameras, we've got a sonar, we've got lots of instrumentation that we can put on and take off.
0:34:57 > 0:35:01This is a very cool toy. I mean, to be able to get a view
0:35:01 > 0:35:05of the river that we would never be able to get as divers is great.
0:35:05 > 0:35:10The other thing is that it doesn't run out of air, it can be down there all day.
0:35:12 > 0:35:16They want to fly the ROV far beyond safe diving range.
0:35:16 > 0:35:20Yep. You've got camera A.
0:35:22 > 0:35:27To help, they're joined by Steve Sargison - specialist ROV pilot.
0:35:27 > 0:35:30He's spent his career salvaging wrecks.
0:35:30 > 0:35:35It's forwards, backwards, go left, go right.
0:35:35 > 0:35:41That will give us full power and that will give us full power up and down, and this is a fine trim.
0:35:41 > 0:35:45The river current runs at three knots.
0:35:45 > 0:35:50The ROV will only just be able to cope.
0:36:01 > 0:36:06The river bed here plunges to more than 90 metres deep.
0:36:13 > 0:36:18This is the moment scientist Doctor Mario de Pinna has dreamt of for years.
0:36:18 > 0:36:22We are here taking the opportunity of coming to these remote places,
0:36:22 > 0:36:26but really the new stuff, the extraordinary stuff, is gonna be in deep waters.
0:36:26 > 0:36:28Yeah, we'll turn it to the right.
0:36:55 > 0:36:59Yes. Rotate to the right a bit.
0:36:59 > 0:37:03- The ROV's first flight reveals a problem.- Just pull it back...
0:37:03 > 0:37:05One of the motors has failed.
0:37:05 > 0:37:09Without full power the ROV cannot descend.
0:37:12 > 0:37:15OK, it's hooked.
0:37:15 > 0:37:21Unless the engine can be fixed, the Abyss will remain tantalisingly out of reach.
0:37:23 > 0:37:27The robot is operating at its limits in a river so deep
0:37:27 > 0:37:31it's a major shipping channel right into the heart of the jungle.
0:37:36 > 0:37:39Steve needs to get to grips with the ROV.
0:37:41 > 0:37:43Time is now precious.
0:37:43 > 0:37:48The team grab a last chance to explore places that will soon be washed out by the rains.
0:37:52 > 0:37:56Mike Pitts is going to look for fish on the forest floor.
0:37:58 > 0:37:59Soon I'll need that camera.
0:37:59 > 0:38:05Further down river, Kate and Mike investigate an area of jungle that is underwater.
0:38:09 > 0:38:14Now the way this is gonna work, is I'll lay down and you drive my feet,
0:38:14 > 0:38:16and that way I don't have to check.
0:38:20 > 0:38:24All right, hold it, let go. I'll kick and see what happens.
0:38:24 > 0:38:32To get steady images of this drowned jungle, Mike improvises a novel form of propulsion.
0:38:37 > 0:38:42Every year vast areas of the forest are flooded.
0:38:42 > 0:38:49The trees and wildlife are perfectly adapted to survive the inundation.
0:38:49 > 0:38:54Fresh water sponges cluster in the branches, waiting to be immersed.
0:38:57 > 0:39:02And fish spill out across the forest floor.
0:39:33 > 0:39:38Mike Pitts is looking for fish that will be high and dry until the floods arrive.
0:39:43 > 0:39:48This jungle has been above water for 3 months, Mike's team is joined by
0:39:48 > 0:39:53a local scientist who's recently discovered unique fish on the forest floor.
0:39:56 > 0:39:59Right, this looks brilliant.
0:39:59 > 0:40:03Any fish here were trapped in pools by the retreating river
0:40:03 > 0:40:07and must endure months in stagnant water before the flood returns.
0:40:07 > 0:40:13- Maybe I think you must... - Some so small they can only be found with a fine meshed net.
0:40:16 > 0:40:17What did you get on there?
0:40:17 > 0:40:21- It is a wolf characin. It bites. - It bites?
0:40:21 > 0:40:24- It's a small predator. - Is that a fully grown specimen?
0:40:24 > 0:40:26- No, it's a juvenile.- A juvenile?
0:40:26 > 0:40:28It will grow up to half a metre long.
0:40:28 > 0:40:30- Half a metre?- Yes.- And it bites?
0:40:30 > 0:40:34- Painfully.- I'm going to release that, there we go. Put him back in.
0:40:36 > 0:40:42But weather permitting, they hope to find an even more remarkable fish.
0:40:42 > 0:40:43Big one.
0:40:43 > 0:40:48On the journey up here Jansen has been explaining to me about the small catfish
0:40:48 > 0:40:53which is probably blind, but lives in this very, very shallow water, or even in the soil.
0:40:53 > 0:40:55It looks like a worm but it's actually
0:40:55 > 0:40:59a fish. It's got feelers, the whole thing, but it's very, very small.
0:40:59 > 0:41:02Big one, yep.
0:41:02 > 0:41:04What's this here? Oh, nothing. Oh, no.
0:41:04 > 0:41:08Yes, that's a fish. Look at that.
0:41:08 > 0:41:09He's pretty red.
0:41:09 > 0:41:11That is it, that's the worm.
0:41:11 > 0:41:13- Or the catfish.- It's a large one.
0:41:13 > 0:41:15- That's a large one?- Yeah.
0:41:15 > 0:41:18If I'd found that by myself, I'd have said that was a worm.
0:41:18 > 0:41:21There's no way I would have said it was a catfish. It has no name.
0:41:21 > 0:41:23No name. It's a new species.
0:41:23 > 0:41:25- A new species.- Undescribed.
0:41:25 > 0:41:28Undescribed and I've got it in my hand.
0:41:28 > 0:41:33The whole of its body can absorb oxygen from the air -
0:41:33 > 0:41:37a miniature catfish that can live on land.
0:41:40 > 0:41:46It has taken all day to fix the robot and they are well behind schedule.
0:41:46 > 0:41:50As night falls, they launch a deep water test dive.
0:41:55 > 0:41:59This is the first ever attempt to reach the Abyss.
0:41:59 > 0:42:00Ready?
0:42:10 > 0:42:12But there's trouble brewing.
0:42:17 > 0:42:22It can become a hazardous situation for the equipment so I hope the storm won't come,
0:42:22 > 0:42:24but if we stop doing things just because of threats
0:42:24 > 0:42:31of storms we'll never do anything here because there is a storm threat in the horizon every ten minutes.
0:42:34 > 0:42:37Suddenly the storm changes direction.
0:42:37 > 0:42:39This is weather that can sink ships.
0:42:39 > 0:42:42Three metres...
0:42:42 > 0:42:442.5.
0:42:44 > 0:42:49Until they get the ROV back on board they're stuck directly in its path.
0:42:49 > 0:42:55The difficulty we have is that the ship will spin on its anchor, we'll get all wrapped around
0:42:55 > 0:42:59with the ROV umbilical and that's when things get a bit nervous.
0:43:05 > 0:43:10It seems the Amazon is conspiring against their mission.
0:43:10 > 0:43:15So much electricity going on up there it's pretty impressive, and you can see
0:43:15 > 0:43:18a different kind of splendour in the Amazon.
0:43:18 > 0:43:20THUNDER BOOMS
0:43:26 > 0:43:29Next morning, there's a break in the weather.
0:43:29 > 0:43:33The robot is launched and descends into the unexplored depths.
0:43:37 > 0:43:38150 feet.
0:43:38 > 0:43:44At last they are poised to find out if there is anything living in the Abyss.
0:43:44 > 0:43:49They're using a bag of fish bait to attract predators from the gloom.
0:43:49 > 0:43:53Scientists know the Amazon is rich with life to a depth of 30 metres,
0:43:53 > 0:43:57but the ROV is well below that.
0:43:57 > 0:44:01We're entering around the realm of as deep as we've dived.
0:44:01 > 0:44:04We got to what? 44?
0:44:04 > 0:44:06- Yeah.- Oh, hang on! We've got a fish coming in.
0:44:06 > 0:44:08Feisty little fella!
0:44:08 > 0:44:12- Straight in there.- Six minutes, we have our first fish.
0:44:12 > 0:44:14- There's two of them.- Two now.
0:44:14 > 0:44:20They've got tiny, tiny, tiny eyes and a big sucker mouth, they look like hag fish.
0:44:20 > 0:44:21Probably vestigial eyes.
0:44:21 > 0:44:23The bait is working.
0:44:23 > 0:44:24Enthusiastic.
0:44:24 > 0:44:27The first sign of life deep in the Amazon.
0:44:27 > 0:44:28Brilliant.
0:44:28 > 0:44:30There's five of them.
0:44:30 > 0:44:34It's getting kind of busy. Look at that. Ah.
0:44:34 > 0:44:37For Mario, a major breakthrough.
0:44:37 > 0:44:43These are scavenging catfish, voracious candiru-acu.
0:44:43 > 0:44:46We have never seen this spectacle before.
0:44:46 > 0:44:50This is the first time I see it. This is wonderful.
0:44:50 > 0:44:53They have huge muscles. The jaw muscles are so big
0:44:53 > 0:44:55that they cover the whole head,
0:44:55 > 0:45:00all the way to the mid line and that's a very, very powerful bite.
0:45:00 > 0:45:03These guys can use a little hole to get inside and eat
0:45:03 > 0:45:11the prey from the inside out, that kind of scares me more than I just have a piece of flesh taken away.
0:45:11 > 0:45:15These scavengers feed on the dead, but can attack the living.
0:45:15 > 0:45:23With a ring of teeth like a ripping circular saw, candiru-acu bore into flesh.
0:45:23 > 0:45:30Fish thriving at 44 metres. But does anything exist in the deepest Abyss?
0:45:32 > 0:45:34They may yet be thwarted.
0:45:36 > 0:45:42The ROV has badly malfunctioned. Steve is forced to do electrical surgery.
0:45:46 > 0:45:48It's going to take some time.
0:45:53 > 0:45:56Next morning, with the further delay
0:45:56 > 0:45:58and just two days of expedition time left,
0:45:58 > 0:46:03Mike grabs a chance to fulfil a personal ambition.
0:46:09 > 0:46:15His search takes him far into the jungle with Amazon guide Samuel.
0:46:15 > 0:46:17They're looking for a sloth.
0:46:19 > 0:46:23It's hard to find them because they crawl in the tree and stay there.
0:46:23 > 0:46:26They don't move much. It's just like a ball.
0:46:26 > 0:46:33If only we can find one of these things cos I really want to see a sloth before I leave the Amazon.
0:46:33 > 0:46:36The fact they move so slowly, they're covered with algae
0:46:36 > 0:46:41and so well camouflaged makes them practically impossible to spot.
0:46:41 > 0:46:47This is ideal habitat for sloth, but it will soon change out of all recognition.
0:46:49 > 0:46:53In the coming months a deluge of rain will flood the jungle.
0:46:55 > 0:46:58It can all happen without ever raining here.
0:46:58 > 0:47:05If it rains up by the Andes or somewhere else and the river just lifts up anyway.
0:47:05 > 0:47:06Every year...
0:47:06 > 0:47:09Phew! That is a lot of water.
0:47:09 > 0:47:14But the sloths will remain high in the canopy above the rising water.
0:47:16 > 0:47:21It takes an experienced eye to spot one in its lofty retreat.
0:47:24 > 0:47:27Right in front of us is a sloth.
0:47:27 > 0:47:29I don't believe it.
0:47:31 > 0:47:33Three toes. Very, very sharp.
0:47:36 > 0:47:37Look at that face.
0:47:37 > 0:47:40Oh, man! That's the greatest face!
0:47:46 > 0:47:52I think more than anything else I just love the way they look and move.
0:47:52 > 0:47:58I wonder if they make decisions at the same pace they climb.
0:48:00 > 0:48:05See, and I don't know why I've had this obsession about seeing a sloth
0:48:05 > 0:48:10while I'm here, but certainly the sloth's unique and I saw my sloth.
0:48:13 > 0:48:17Mike has realised a lifelong ambition,
0:48:17 > 0:48:21but the expedition's main objective is still to be achieved.
0:48:21 > 0:48:24At last, the robot has been repaired.
0:48:24 > 0:48:29Fresh bait is secured... and quality-tested!
0:48:29 > 0:48:32They have only two nights left
0:48:32 > 0:48:35and storms could shut them down at any time.
0:48:41 > 0:48:45They must quickly launch into the Abyss again.
0:48:52 > 0:48:55The robot is primed for its deepest dive yet.
0:49:01 > 0:49:06It's descending smoothly, dropping down towards the river floor far below.
0:49:10 > 0:49:15No camera has ever pryed this deep in the Amazon before.
0:49:15 > 0:49:17This is in a river.
0:49:17 > 0:49:19This is in the middle of the Rio Negro.
0:49:19 > 0:49:22250 feet - unbelievable.
0:49:22 > 0:49:28To increase the chance of attracting fish in the greatest depths, they have switched to a low light camera.
0:49:31 > 0:49:34Now all they can do is wait.
0:49:40 > 0:49:43For five hours, nothing.
0:49:43 > 0:49:48Then suddenly from the darkness the ghostly images of candiru-acu appear.
0:49:48 > 0:49:53This is the first time anyone sees images of fish at 85 metres down.
0:49:53 > 0:49:55- Look.- They're going bananas.
0:49:55 > 0:49:58There is life in the Abyss after all.
0:49:58 > 0:50:00The 65 metre trap.
0:50:00 > 0:50:02Yeah, this is the same species.
0:50:02 > 0:50:04Look at that, look at that!
0:50:04 > 0:50:08- Oh, that's beauty.- Who is that?
0:50:08 > 0:50:14It's another catfish that's also, it's partly a scavenger although not to the same degree as the candiru.
0:50:14 > 0:50:18I mean, did you know that candiru would be eating and feeding at 85 metres?
0:50:18 > 0:50:23No, I didn't expect that life below 30 metres would be that rich.
0:50:23 > 0:50:26- What's that?- That's great.
0:50:26 > 0:50:30A relative of the candiru-acu, but even larger and more voracious.
0:50:30 > 0:50:33That did not look the same. Who was that?
0:50:33 > 0:50:38- Is that a different candiru? - Yes, that's a Cetopsis coecutiens -
0:50:38 > 0:50:41its scientific name. That's really different.
0:50:41 > 0:50:44- It looked like a shark. - The little ones are gone.
0:50:44 > 0:50:48It's a beautiful fish. It's silvery, it has a long dorsal fin.
0:50:48 > 0:50:50And did you guys notice the difference...?
0:50:50 > 0:50:55There it is. It comes, grabs a big chunk of flesh and swims away.
0:50:55 > 0:50:58It doesn't stay like spinning around and trying to grab it.
0:50:59 > 0:51:02They've revealed that the Abyss swarms with life.
0:51:04 > 0:51:08Scavengers waiting for anything the river brings them.
0:51:11 > 0:51:16It's amazing. It's really... These images are something really original.
0:51:21 > 0:51:25It's the expedition's final day.
0:51:25 > 0:51:32To get better pictures, the team decide to risk sending in the divers with their high tech cameras.
0:51:34 > 0:51:37They are on the very edge of the Abyss.
0:51:44 > 0:51:50There's a narrow shelf within diving range, but is it in candiru-acu territory?
0:51:50 > 0:51:56No-one has gone face to face with these voracious scavengers before.
0:51:56 > 0:52:01The divers are preparing for an encounter that could be dangerous.
0:52:01 > 0:52:06If one bit you, you'd start bleeding quite profusely and that could attract the others.
0:52:06 > 0:52:11Before you know, you've got a situation where you've got to get out quick.
0:52:11 > 0:52:17So we're all wearing a 3mm suit, gloves, hoody and a mask on top, so we're all protected.
0:52:17 > 0:52:20If the bait attracts candiru-acu,
0:52:20 > 0:52:23once in the water there will be no going back.
0:52:23 > 0:52:25Let's go.
0:52:26 > 0:52:28ROV is now on the bottom.
0:52:28 > 0:52:31Thrusters are disabled.
0:53:03 > 0:53:05Thunderstorms threaten nearby.
0:53:05 > 0:53:10If they come much closer they will have to abort the dive.
0:53:16 > 0:53:19After 40 minutes, there's still no sign of any creatures.
0:53:24 > 0:53:27Is it too shallow after all?
0:53:27 > 0:53:30Don't waft that light on it.
0:53:30 > 0:53:33Whoa! It would appear... Oh, there's one right there.
0:53:33 > 0:53:40There's two in front of me now. As a matter of fact there's of them. One is hitting my backside.
0:53:40 > 0:53:43They're very energetic, it's as though
0:53:43 > 0:53:48they think this meal isn't gonna last long. I better take advantage of it while I can.
0:53:49 > 0:53:54Nearly blind, candiru-acu tracks its prey by scent.
0:53:54 > 0:53:59Its streamlined body allows it to writhe, gorging inside its victim.
0:54:01 > 0:54:06I can tell you this, things are starting to heat up. We now have
0:54:06 > 0:54:10candiru all going after this fish in front of me, grabbing it and twisting
0:54:10 > 0:54:17and turning. They're going after the fish so enthusiastically that there's no way I could get this close
0:54:17 > 0:54:19if I wasn't wearing this helmet.
0:54:22 > 0:54:27They've eaten a hole in the top of the fish, now they're popping through the skin. It's amazing.
0:54:27 > 0:54:30So are they eating it from the inside out?
0:54:30 > 0:54:32Looks like maggots.
0:54:32 > 0:54:37Yes, I would say they are eating it from the inside out.
0:54:37 > 0:54:40Oh, my gosh! They're going after my stomach belt.
0:54:40 > 0:54:44They're getting just a little bit too close for comfort.
0:54:44 > 0:54:51Perhaps only their wet suits are saving the divers, in water infested with candiru-acu.
0:54:53 > 0:54:57Although the reputation of the piranha is legendary,
0:54:57 > 0:55:01could it be that these are the true monsters of the Amazon?
0:55:01 > 0:55:06I'm just glad that these are scavengers and not predators
0:55:06 > 0:55:11because I can't imagine that piranha are any more aggressive
0:55:11 > 0:55:13than the candiru.
0:55:14 > 0:55:16THUNDER ROLLS
0:55:16 > 0:55:21The weather topside is deteriorating fast.
0:55:21 > 0:55:24I'm gonna leave now and I'm gonna go back up because
0:55:24 > 0:55:28this has been quite an experience and I want it to remain a good one.
0:55:28 > 0:55:32OK. We will see you at the surface. Everyone here is standing by.
0:55:34 > 0:55:36They're on the surface.
0:55:36 > 0:55:39Going to extinguish the light now.
0:55:39 > 0:55:40There we go.
0:55:41 > 0:55:43Yeah, you're there.
0:55:43 > 0:55:45- Woah.- You OK?
0:55:45 > 0:55:49Holy cow! If I had known about that
0:55:49 > 0:55:54when I first came here I would have worn chain mail on every dive.
0:55:54 > 0:55:57You don't dare go down with a cut.
0:55:57 > 0:56:00I mean, they are just...
0:56:03 > 0:56:07It was quite dramatic and I've done many, many dives all over the world
0:56:07 > 0:56:11and I think that has to go down as one of the most disturbing.
0:56:11 > 0:56:14They have good reason for their concerns.
0:56:14 > 0:56:17Candiru-acu are tenacious to the extreme.
0:56:17 > 0:56:19They're still in it.
0:56:19 > 0:56:24They continue to devour the bait even when it's back above water.
0:56:24 > 0:56:26Look at it now!
0:56:29 > 0:56:32The expedition is nearly over.
0:56:32 > 0:56:37In five short weeks, the 50 team members have voyaged 3,000 kilometres.
0:56:40 > 0:56:46They've experienced the incredible variety of Amazon wildlife at first hand.
0:56:46 > 0:56:48That was pretty spectacular.
0:56:48 > 0:56:50That was a good, fun dive.
0:56:52 > 0:56:55All right, let's find some fish!
0:56:57 > 0:57:02Over 100 species have been filmed, many for the first time.
0:57:08 > 0:57:13They've discovered fish completely new to science,
0:57:13 > 0:57:17but all this is only scratching the surface.
0:57:17 > 0:57:22There are thought to be another 2,000 species still to be recorded.
0:57:25 > 0:57:27In this eerie world of the strange,
0:57:27 > 0:57:32who knows what extraordinary creatures may yet be found?