Original subtitles

in the Last Frontier, Alaska.

[Jessica cheering]

[Josh] Jess and Phil investigate new reports of an aquatic beast

believed to inhabit these waters.

How big do you suspect this creature is?

Up to over 50 feet.

She looks at me and looks back at the lake and says,

"What the F is that?"

-Nobody has ever laid eyes on this. -[Jessica] Mmm-hmm.

[Phil] Ever.

[Josh] Now, my team is launching an arsenal of modern technology...

[Phil] All right. Going in.

[Josh] ...to get to the bottom...

[Phil] Tons of salmon right there.

[Josh] ...of what lurks in the frigid depths.

Hang on!

It's getting really murky down there.

[Jessica] What's this, what's this?

-Oh, my God! -Oh,[bleep].

That's big, that's dark.

What is that?

[Josh reading]

My name is Josh Gates.

In my travels, I've experienced strange things

that defy logic and made me question everything.

Oh, my God.

Now, I've put together a team to investigate

the stranger side of the unknown.

Let's go.

[Josh] Phil Torres is a scientist

who hunts for rational explanations.

[Phil speaking]

[Josh] Jessica Chobot's paranormal research has made her a true believer.

If you're here with us, knock again.

[Josh] Together, we're searching for answers...

[Phil] What is happening here, Jess?

[Josh] ...to the world's most extraordinary mysteries.

This isExpedition X.

All right, Phil, Jess, for your next investigation,

I am sending you to a place that is as remote as it gets.

-Uh-oh. -I like the sound of this.

In fact, it is so remote and so wild that you are probably going to need this.

And you know what? Maybe even this.

Bear spray, huh?

-That is a lot of bear spray. -[Josh] Sure is.

That's because there are a lot of bears there.

In fact, it's home to the largest brown bear population on Earth

and not coincidentally,

the largest red salmon population on Earth.

Ooh, I think I got this one, Jess.

-We're going to Alaska. -[Josh] That's right.

We're going to Alaska! That is actually pretty cool.

I'm actually surprised that it took you this long to send us there,

because it is like a magnet for the unexplained.

It's true.

There's a lot of weird stories in Alaska, but in this particular case,

we're talking about something that many native Alaskans

and in fact some scientists even insist is absolutely real.

A large, unidentified creature that supposedly lives in a 1,000-foot deep lake.

[Josh] Iliamna is the largest lake in the Last Frontier,

sitting in southern Alaska and connected to the Bering Sea.

It has been a life source to the indigenous people living along its shores

for nearly 10,000 years,

providing food and allowing them to build an economy

around the abundant salmon.

But for generations, the Alaska Natives have claimed

there's more than just fish swimming in Iliamna.

Local Tlingit legends describe a 30-foot aquatic beast

with a wolf-like head and razor sharp teeth.

They call it the Gonakadet.

To the Aleut people, it is known as the Jig-ik-nak,

an aggressive predator that stalks these frigid waters,

hunting its prey.

-[groans] -[Josh] Be it animal or human.

Local lore says the creature attacks fishermen,

specifically targeting boats painted red.

[dramatic music playing]

[Josh] In the 1940s,

with increased airplane traffic over Alaska,

comes a dramatic surge in sightings by bush pilots,

of a dark-colored oversized beast in the lake.

In 1963,

a biologist from Alaska Fish and Game spots what he describes

as a 30-foot long creature, cruising below the surface.

In that same decade, NASA astronauts report similar sightings

while conducting training flights around the lake.

By 1980,

reports of a mystery creature up to 50 feet long becomes so prevalent

that an Anchorage newspaper offers a $100,000 reward

for solid proof of the Iliamna Lake Monster.

The reward never pays out, but the reports persist.

Now, a spate of recent sightings has attracted the attention

of the state's fisheries commission.

The office keeps an open file to document the reports,

and two biologists are so convinced there's a unique species here,

they've started their own investigation

and believe they're close to solving the mystery.

So does that reward still stand,

'cause I'll split it with you?

60, 20, 20. Right?

I said you, Josh.

All right. Cool. Sure. 60-40.

-You watch yourself, Jess. -What?

[Josh] So what do you guys think?

Well, I think that legends like this always come from truth,

and this is a perfect example.

A lot of eyewitnesses have seen this over a long period of time,

so it's not a matter of if there's something living in this lake,

it's a matter of us going out there and finding it.

I agree with you there, Jess.

I think there's something in the lake,

but that doesn't mean that something is a lake monster.

It could be an overgrown fish.

It could be a school of fish that come up to the surface. We don't know.

But that's also why I think it's kind of awesome

that there's a team of scientists there,

dedicating energy to try to solve this.

Well, I'm glad you feel that way,

because you're going to be joining forces with those scientists.

They are up at the lake right now doing research,

trying to figure out what this thing is,

and they have a limited window

because Lake Iliamna freezes over in the winter.

Now they've been using stationary underwater cameras.

What they don't have is an ROV.

So we're going to help them with that.

Hopefully the ability to maneuver around underwater

and get real-time video back might give us a breakthrough.

Awesome. I'm all over that ROV.

-Video game geek gets to drive. -Yes.

[Phil] No complaints there.

[Josh] So the mission is simple.

Get to Iliamna Lake and figure out what people are seeing.

Could this be some sort of uncatalogued species

that natives have been witnessing for generations?

Or is this simply a case of misidentification of a known animal?

We're going to find the lake monster. I feel it in my bones.

-I like the confidence, Jess. -[Jessica] Thank you.

I like the confidence. Also, don't get eaten by a bear.

-Oh, hold onto these. -Good luck.

[Josh] Phil and Jess fly nearly 3,400 miles

to Alaska's largest city, Anchorage.

There, they connect with local pilot Tim La Porte,

who's been transporting passengers and supplies

to and from Iliamna for 45 years in his fleet of PC-12s.

To travel more nimbly to this remote location

and to stay under our aircraft's strict 2,500-pound weight limit,

we've downsized the gear and the crew.

[Tim] Hope everybody had a light breakfast.

[dramatic music playing]

[Phil speaking]

-[Tim speaking] -[laughs]

[Phil speaking]

[Jessica speaking]

[Josh] Alaska roads will only take you so far

over this rugged undeveloped landscape.

So this small plane will carry our intrepid adventurers the remaining 200 miles

to Iliamna on their hunt for a monster.

[Phil speaking]

[Tim speaking]

[Jessica speaking]

[Tim speaking]

[Phil speaking]

[Tim speaking]

[Phil speaking]

[Tim speaking]

[Phil speaking]

[Jessica speaking]

[Josh] Situated on the Alaska Peninsula,

Iliamna Lake is 77 miles long and 22 miles across at its widest point.

The 1,000-square-mile lake connects to Bristol Bay and the Bering Sea.

The average depth is around 150 feet, but in some spots,

it gets down to a thousand feet,

water deep enough to submerge the Eiffel Tower.

[Phil speaking]

[Tim speaking]

[Josh] Phil and Jess land at the Iliamna airport

and hop on the ground transportation

I've lined up to get them across the village.

[engines revving]

[adventurous music playing]

[Josh] Around here, cars are scarce and the roads are just a little bumpy.

[Jessica cheering]

[Phil] Living in Alaska means sharing your backyard with moose,

caribou and wolves,

not to mention the brown bears that greatly outnumber humans here.

[Jessica] It's pretty beautiful back here.

[Phil] Yeah, it is.

[Phil] At Iliamna, the power ratio is clear.

Nature rules, people just try to survive.

And if we get hurt out here, we're on our own.

[Josh] I've arranged for Phil and Jess

to meet Bruce Wright and Mark Stigar at their base of operations.

They're a pair of real-life Captain Ahabs, hell-bent on finding their white whale

or, in this case, their dark lake monster.

Bruce was a biologist with Alaska Fish and Game and continues to study

the state's ecological habitats.

Mark has a degree in wildlife biology and is a retired colonel

and former chief aviation officer

for the Alaska Army National Guard.

Nice to meet a fellow biologist.

Interested to see what you guys can teach us about

whatever's out there in the lake.

How big do you suspect this creature is?

Well, there's... there's lots of different reports, I mean, up to over 50 feet.

[Jessica] That's crazy. What would something like that even eat?

We have five million sockeye salmon

that come up to the lake on an average year,

and each of the females lays 2,000 to 5,000 eggs.

So now you're looking at maybe five, six billion salmon in the lake rearing,

and we know we have northern pike, burbot, lake trout,

all these other predatory fish out there.

[Jessica] Meaning there's plenty of fish here to sustain a monster.

So you're saying there's a top predator in the water

and we don't know what it is yet.

-We first started off trying to catch this thing. -[Jessica] Mmm-hmm.

[Bruce] We thought, "Well, if we catch it, we would know."

And we would set down up to 15 hooks, we were using a 38-pound anchor

and we'd put it on the bottom, baited with a full salmon head.

We had planned to only leave it out overnight,

but due to the weather, couldn't get back to it.

When we did come back to it, as I was slowly coming in to retrieve the line,

I noticed that the line was not going out the same way that we had put it out.

And it actually had moved quite a bit.

And we started pulling the lineup, and the line was just totally tangled up.

Several of the hooks are gone, and of the 14 fish heads, ten of them were gone.

And the 38-pound anchor was dragged 50 yards.

-[Jessica] Oh, wow. -So...

-So this thing is strong. -Yeah.

So at that point, I absolutely knew there was something in this lake.

[Jessica] So then what do you think it is?

[Mark] I'm not sure what it is.

There's large shark predators out there. One is the seals.

We know there's freshwater seals

that live in the lake year-round.

I think that's something else.

[Phil] I mean, seals are marine mammals.

That, to me, says that there's something unique about this lake.

If the seal is a resident here,

and essentially shouldn't be based on the biology we know

of seals around the world, what else could be a resident here

that shouldn't be here?

A lot of unknowns up here.

[Jessica] Our plan is to head towards the eastern side of the lake,

where Mark says something sizable destroyed his bait system.

Locals say the monster is aggressive and territorial,

so maybe whatever attacked their rig could still be in the area.

Summer in southern Alaska brings about 19 hours of daylight,

and even when the sun sets, it'll remain low in the sky.

That should give us a lot of extra light for this investigation.

[Mark] We did a recon a few days ago,

we saw some targets on our acoustic gear that were really intriguing.

We're trying to decipher if they were salmon or if they were something bigger.

[Phil] Sure, a tightly grouped school

of fish could look like one large mass on the sonar,

but with some reports claiming the mystery creature is upwards of 50 feet long,

the first place my biologist brain goes is whale.

Whales can reach that length, but this is a freshwater lake.

Even if a whale could survive in fresh water,

could it get here from the Bering Sea?

People have claimed to see beluga whales in Iliamna.

Now they don't grow much past 15 feet.

But if a beluga could somehow find its way here and survive, maybe a larger whale can, too.

So this is close to where Tim, our pilot, saw it as well.

Getting close.

Little bit of a hotspot for all the sightings.

[Jessica] The first thing overboard

is going to be Bruce and Mark's camera trap.

We attach a waterproof camera to this baited metal cage and then tie a buoy to it.

If anything swims this way looking for a meal,

the camera should capture images

that we'll be able to retrieve from the memory card.

All right, well, let's grab the ROV.

[Jessica] But the ROV is the main event.

It's got an onboard 4K ultra high definition camera

and a row of LED lights to help us see in the murky waters.

This will be the first time anyone has used

this tech in these waters to search for the creature.

And Bruce believes it's just the tool he needs to finally get a visual on it.

[Phil] That's a good view.

All the sediments we're seeing in the water, that's plankton.

All of this is phytoplankton, it's algae.

That's why this thing is so productive, this lake.

[Phil] Holy[bleep], look at all those fish. Well, that's a good sign.

[Jessica] That's a very good sign.

[Phil] Where there's fish, there's something that eats fish.

[Mark] We got a big target at 40 feet.

[Bruce] Big target at 40 feet? How big?

[Mark] It's hard to tell, but it's moving.

[Jessica] I'm not seeing anything yet.

-What's that? -That.

[gasps]

[tense music playing]

-What's that? -That.

[gasps]

[Phil] Is that what we saw on the sonar?

[Jessica] Something just hit the ROV.

What is that?

So what's dragging me? Look at this.

That is weird.

All right. Let's let the line go, and let's see.

Keep going up, keep going up.

[Jessica] I'm pushing it, it's not going up.

It just keeps dropping. It's not responding at all.

[Jessica] The camera's working, but the motor is shot,

literally dead in the water.

I think it's possible our ROV was attacked

by something that saw it as either a threat or a snack.

I don't understand why it's not going up.

[Phil] Despite Jess's mad video gaming skills,

I think operator error might have had

something to do with the ROV going down.

But for argument's sake,

let's say something near the lake floor did mess with it.

Could it have been a sturgeon?

Sturgeon can live 100 years and grow to 20 feet long,

which makes them some of the world's oldest and largest freshwater fish.

These bottom feeders aren't supposed to be in this lake,

but they can be found in some southern Alaskan rivers.

If a sturgeon did manage to make it to Iliamna,

I can see how something that size in shallower water

could get mistaken for a monster,

especially from up in a plane, like many of the reports.

-All right. ROV's out of the water. -All right, good.

[Jessica] Before we leave with our busted robot,

we check Mark and Bruce's underwater camera.

Maybe it snapped a shot of whatever was messing with our ROV, but no dice.

So we drop it back in the water, hoping our luck changes.

[Jessica] The next morning, Mark and Bruce

are setting out more of their baited cameras in other parts of the lake.

While they tackle that, there's an experiment I want to try.

All right. You want to head towards that red box over there?

[Phil] Yeah.

[Jessica] Legend says the lake monster is drawn to the color red,

even attacking red-bottomed boats.

[sinister music playing]

[Jessica] I'm going to put that part of the legend to the test

at a section of the lake,

where there have been recent sightings from people on shore.

So your idea is that this is the color that the locals claim

the lake monster's attracted to.

-Exactly. -And that's why they don't use red boats like this.

And it makes sense, because the salmon here are red.

-[Phil] Okay. -And that's its food source.

So if it's attracted to that color, because of its food source,

maybe it'll be attracted to this kayak, because it's the same color.

Okay.

[Phil] I'm not saying there's a lake monster out here attacking red-bottomed boats,

but research shows that even though they might not have

the ability to actually distinguish colors,

some marine life do appear to gravitate to certain colors.

Sharks are often drawn to high contrast colors like yellow, orange and red.

So who knows?

Jess's experiment might not be as crazy as it sounds.

So if we put this in the water,

attach a trail cam to that red box over there,

maybe we can get it to breach and we'll be able to capture it on the game cam.

Yeah.

Yeah. One more thing you're going to like Phil.

[Phil] What you got?

Mini seismometer.

Ooh!

So that if anything hits this, as if it was attacking it,

we will be able to register it on this.

[Phil] Nice.

[Jessica] I figure we can put this down here

so that if anything hits from the bottom up, we'll be able to get it.

Oh, lighting up. Check it.

[Jessica] Yeah, very nice.

[Phil] Yeah.

[Jessica] If there's any sudden movement of the kayak,

this device will record it and send an alert to my phone.

-Cool. -[Phil] On.

-On. -[Phil] Okay.

Let's get the kayak in the water.

Out she goes.

[Jessica] Nice.

Leave it out here overnight and get it in the morning?

-[Phil] Let's do it. -All right.

[Phil] Jess's experiment gets me thinking,

if the mystery creature is somehow drawn to red,

"Is it possible that what we're looking for

is some kind of shark that made its way upriver?"

There are sharks that can survive in fresh water.

The most common shark in the Bering Sea is the Pacific sleeper shark.

Sleeper sharks are dark-colored

and have been known to reach upwards of 20 feet and 8,000 pounds.

They've never been officially documented around Iliamna Lake,

but I need to consider all options.

If a shark is around here, where's the best place to find it?

The Newhalen is a 22-mile river that flows south into Iliamna Lake.

We're told it's a major pathway for a mind-boggling migration

of sockeye salmon and rainbow trout.

So we've arranged for some high speed transport to navigate this epic waterway.

[Phil] I'm guessing you're Captain John.

Yeah.

-[Phil] Are you going to take us upriver? -[John] I am.

All right.

What should we expect? Are we about to get wet?

Possibly. We'll try not to.

Try not to go overboard.

-[John laughs] -Yeah.

Try not to push you.

[Jessica] Hmm.

[dramatic music playing]

So have you ever seen a weird wake,

just naturally, just like one big wave coming in?

[John] Absolutely.

You may see something above the water,

you know, associated with the wake.

What does that mean?

That's the million-dollar question.

I guess the question here is, is it a lake monster or is it a wake monster?

Oh, my God!

Can we kick him off the boat?

[adventurous music playing]

[Phil] Yes, it is impressive how much water is going through here.

[Jessica] Yeah.

[Jessica] With its sturdy aluminum hull,

unique sled-shaped bow and high performance engine,

Captain John's custom-made boat is perfectly designed

to maneuver through shallow, rocky waters,

getting us into remote areas inaccessible to many other boats.

Rocky rapids coming up, right ahead.

[adventurous music playing]

[Phil] This is insane.

[Jessica] This is awesome.

[Phil] We've been flying over the rapid.

We had no idea, a boat like this could get up a river like this.

You have done this before, right?

Yep.

[bleep]. This is insane. Oh!

-[Jessica] Oh! -[Phil] Whoo!

You're going between that?

Hopefully.

[Jessica] Oh!

[Phil] Oh, my God!

You're going between that?

Hopefully.

[Phil] No way.

Hang on!

Woo-hoo-hoo.

Oh, my God!

That was insane.

If I was a lake monster, I'd do this for fun.

[Phil] Oh, yeah.

Full of delicious salmon. You just open your mouth, you get a bite.

[Jessica] Yeah.

[Phil] As we skim over the rapids,

I scan for any signs of a large aquatic predator.

While Jess is looking for a lake monster behind the local lore,

I'm trying to stay open-minded on what known species it could possibly be,

an overgrown fish like a sturgeon

or even a rogue shark or a whale

that found its way up here from the Bering Sea.

Oh, my God!

-[Jessica] Oh, wow. Look at them all. -[Phil] That is all fish.

Tons of salmon right there.

[Phil] No doubt, this river is an all-you-can-eat buffet.

Just ask the bears.

[Phil] We got a bear! We got a bear!

Right on the edge up here.

[Jessica] Oh, yeah!

[Phil] So the bears here get absolutely enormous,

because there's so much salmon, so much to eat,

they can get up to 1,500 pounds.

So that is just a perfect example of that,

predators get big in this area.

[Jessica] Ooh, a bald eagle. Here she comes.

[Phil] Wow. How about that?

[Jessica] That's cool.

[Phil] We've now spotted two apex predators

that feast on the abundant fish in this river.

But I'm not seeing any signs of anything big living in the water.

And when that water turns into Class V rapids...

[Phil] Holy [bleep], it's insane.

[Phil] ...we decided to get out and assess

from a different vantage point.

[Jessica] Oh, my God, look at this!

[Phil] Whoo!

Wow!

Come on.

[Jessica] Oh, check it out, you can see all the salmon over there.

Oh, yeah, they're all concentrated right there.

I will say, trying to fight against something like this,

that'd be tough.

[Jessica] I mean, I think it's possible it could be coming up this river to feed,

but it wouldn't stay here too long. Not in these rapids.

[Phil] Jess and I agree that this river is too shallow

and too rough for a big aquatic creature.

My guess is it lays dormant

in the deep end of the lake and pops up when it needs to feed.

Yeah. If something's hiding, it's going to be hiding in the depth.

Yeah.

So should we get out of here before we get eaten by a bear?

-Yeah, I'd like that. -Okay.

[Jessica] When considering the plausibility of a lake monster,

scientists say it would need two basic things to survive,

plenty of food and a suitable environment

where it could stay hidden.

Skeptics of the legendary Loch Ness Monster cite the lack of fish

in Loch Ness to sustain what would be Nessie's oversized appetite.

But that's obviously not a problem in Iliamna.

As for a place to stay hidden,

my research reveals stories told by native elders,

who believe the creature makes its home in underwater caverns

found in the deeper parts of the lake.

But with a broken ROV and depths that are too great to dive,

we have no way to look for those caves.

We're gonna need some help.

[Josh] Hey, guys, how are you?

-Hi. -Hey, Josh.

How's the Last Frontier treating you?

It's gorgeous out here.

[Phil] But I'll tell you what, Lake Iliamna,

there's something special about this place.

It is giant. It is deep. It is remote.

It is arguably the most well-preserved large lake on this hemisphere.

Yeah, great. Have you caught the lake monster yet, Phil?

-Mmm. -Not quite.

Okay. Any idea what people are seeing there?

I'd say we have a list of suspects out here.

It could be a large fish, it could be a sleeper shark,

or it could be some other thing.

We're trying to narrow it down.

Sleeper shark?

Okay, well, I've got something that might help reel in your investigation.

I've tracked down a new lead that I want you to follow up on.

It's a pair of sisters that just came forward

claiming they spotted the lake monster near their village.

Not only that,

they even managed to capture a video of what they saw.

[Jessica] Wow, really?

[Phil] We also need your help with something else.

Bruce and Mark, the biologists we teamed up with here,

are so excited that we have an ROV,

and for the first time ever, they were able to see

a live feed of what's down below.

[Jessica] Yeah, until the lake monster attacked it.

[Josh] Wait, what?

[Phil] Either that or Jess crashed it on the bottom.

[Josh] Chobot!

[Jessica] Here's the thing.

I found stories that the creature lives deep in underwater caves,

so if we can find those caves...

[Phil] Long story short, we need an ROV now more than ever.

Well, a replacement ROV in a hurry,

considering where you are, bit of a tall order,

also I'm not sure I trust you anymore,

but I will make some calls, see what I can come up with.

In the meantime, go talk to those witnesses, okay?

Sounds good.

-Bye. -See you, Josh.

[Jessica] The next morning, we meet sisters, Christina and Alexanna Salmon,

prominent members

of their Village Tribal Council

and whose family has lived on the shores of Iliamna for generations.

So it was right here, this is where you saw it?

-Yes, from here. -Okay.

[Alexanna] It was in the lake.

[Christina] Right where the boat is right there.

-[Alexanna] Yes. -[Phil] Okay.

But it was way bigger than that boat.

Okay. You got to walk us through from the beginning.

[Jessica] Yeah.

Okay. I came up and we're visiting right here.

And, um, just like right now talking to you,

you could see something moving.

And she looks at me and looks back at the lake

and says, "What the F is that?"

[Alexanna] My mind was trying to justify what I was seeing.

Pretend it was a submarine that could bend and turn.

[Phil] So it was just plowing straight.

So submarine was coming straight and then turned.

And at that point, we saw a big black hump,

as it was like diving back under

and it's just parted the water as it went.

[Phil] Now, I understand you have footage of this thing.

[Alexanna] Yes.

[Phil] Whoa. Look at that.

Now, I understand you have footage of this thing.

[Alexanna] Yes.

[Phil] Whoa. Look at that.

[Jessica] Wow, look at the size of that wake.

[Jessica] The sisters' video is compelling,

but it's not exactly the concrete proof

of an aquatic monster I was hoping for.

According to their testimony,

by the time they whipped out a phone and hit record on the camera,

they only managed to capture the very end of the sighting.

But even that five seconds of video shows something leaving an impressive wake.

So you actually saw it kind of crest, like come out of the water a little bit?

[Alexanna] Oh, yes.

When we saw it, it was like a pure black, shiny, it looked like a whale.

So was it a whale?

There is no way a whale could have made it up the river

with no one seeing it.

It was something you've heard about your whole life.

What have you, what have you heard?

A lot of the elders have had sightings of it,

and they've always described it as big and gray.

-That's cool. -So there's something in the water here.

-[Christina] Yeah. -There's got to be.

[Jessica] I believe the sisters had a chance sighting of the creature,

as it made a rare breach of the surface.

But if we want to see it for ourselves,

we have to go to where it lives.

We meet back up with Bruce and Mark,

who've been busy placing underwater camera traps throughout the lake.

We'll check the cameras later, but right now, we need to find these legendary caves.

You could see caves on some of the islands, as you go around.

So maybe there's caves down below.

The lake's pretty deep over here.

And then there's been sightings all up in... in this area.

[Phil] Iliamna Lake sits on the northern edge of the Pacific Ring of Fire,

meaning the topography here is the result of earthquakes,

volcanic activity or glaciation,

any of which could create caves and tunnels,

AKA hiding spots for a large animal.

To help us find them,

Josh came through with a special delivery from Anchorage,

a state-of-the-art ROV and a seasoned pilot to boot.

Sorry, Jess.

[Phil] Welcome to the team.

-Yeah, it's a beautiful day to go on a boat ride. -[Jessica] Yeah.

You do know what we're going for here.

I know that it's a monster.

I guess technically we don't know what we're going for here.

-I mean, yeah. -But we know it's big.

But no one's been able to actually get this thing on tape,

especially underwater.

So that's where we hope you and your skills can help us out.

-Who knows what we'll see? -I know.

All right. Let's hit it.

[Jessica] We hightail it across the lake,

traveling about 18 miles east to the search area Bruce pointed out on the map.

You don't want direct sunlight when you're sending down an ROV,

because that sunlight bounces off

the particles in the water and can actually make it harder to see.

So having this fog overhead, it's not too hot out, conditions looking good.

[Jessica] Bruce and Mark have identified several small rocky islands

scattered in this corner of the lake

that could be an indication of caves down below.

[Phil] Definitely see what look like caves over there.

We need to get our ROV in there.

[Phil] Jess is all in on the ROV finding caves where a monster might live,

but I'll be using it to search for something that could be mistaken for a monster.

To help with that hunt, Bruce breaks out another trick of the trade.

[Bruce] This little thing right here

is called the Mako magnet, puts out a low frequency.

-[Jessica] Mmm-hmm. -Injured fish sound.

So this thing puts out a low frequency noise that goes how far out?

More than a mile.

We could potentially bring in the lake monster.

[Bruce] We don't know.

[Phil] We attach a waterproof camera to the Mako magnet's cage.

Let's get this up on the ledge.

And to maximize our coverage all around the boat...

All right, going in.

...down go the rest of our submersible cameras.

If the Mako magnet attracts something,

we'll get a shot of it, no matter where it approaches from.

Now we just got to get a robot in the water.

[Phil] With about $45,000 worth

of high-tech features built into it,

this ROV is one of the most advanced underwater vehicles on the market,

hence the need for a specially trained pilot.

This robot can safely reach depths of a 1,000 feet.

A lot of other ROVs would be crushed by the pressure.

How's the video feed looking?

[Jessica] It looks good.

The plan is to navigate towards the island

in search of rocky caves and ledges,

where a large monster could potentially hide.

[Jessica] It is a little cloudier over on this side, though.

What is, what is that back there?

[Jessica] Looks like a car bumper.

Maybe it's an airplane.

[Jessica] Oh, it could be a piece of an airplane, maybe.

[Bob] It does look metal.

-I mean, it could also be a branch. -I mean, it looks metallic.

-But it's got a... -It does look like a branch,

but right now, it looks like...

I think that's a branch.

-[Jessica] You think that's a branch? -[Phil] Yeah.

It's getting really murky down there.

-Big tree. -[Jessica] A whole bunch of trees.

[Jessica] Look at that. That's a cliff's edge.

Wow. This is wild.

Look at that.

I'm going to go out away from the wall

and then turn around and look back.

[Jessica] Okay.

[Phil] Wow, look at that structure.

It's crazy nobody has ever laid eyes on this.

-[Jessica] Mmm-hmm. -Ever.

Oh, my gosh.

That's incredible.

Wow.

[Bob] We're at 126 feet.

[Jessica] Twenty-six.

-Let's just keep going. -[Jessica] Keep going, because...

-Yes. -No one has been down here.

[Mark] Big target showing up on the sonar right now, about 150 feet down.

[Phil] Let's keep heading down that cliff.

[intense music playing]

[Jessica] What's this, what's this, what's this?

[Phil] Whoa!

Looking for a shark in Iliamna Lake might not be so farfetched,

because even though sharks typically live in the ocean,

certain species have the ability to retain or recycle salt.

The Ganges shark, as its name suggests,

inhabits the bustling rivers of India.

The speartooth shark can be found in the tropical riverbeds and estuaries

of Papua New Guinea and northern Australia.

Then there's the meanest of the bunch, the bull shark.

This aggressive apex predator can swim hundreds of miles upriver.

It's been documented in the Mississippi,

as far north as Illinois and in Louisiana's Lake Pontchartrain.

And some believe it was a bull shark and not a great white

that famously terrorized the New Jersey Creek in 1916

and later inspired my favorite beach read, Jaws,

meaning they could be hungrily hanging out

in a freshwater lake or river near you.

[intense music playing]

[Mark] Big target showing up on the sonar right now, about 150 feet down.

[Phil] Let's keep heading down that cliff.

[Jessica] What's this, what's this, what's this?

[Phil] Whoa!

That's big, that's dark.

What is that?

[intense music playing]

[Jessica] Do you still see anything on the sonar?

[Mark] Not anymore.

Down to 170 feet.

[Jessica] Still straight drop, too.

If we can find a deep water cave,

we may answer the question how an aquatic giant has managed to escape discovery.

[Phil] 200 feet down.

Is that starting to flatten out?

Yeah, it looks totally different over here.

[Phil] 220.

240. Keep going.

[Jessica] Oh!

That looks cool.

Just look around.

Look at those lines.

-[Bob] Tracks. -[Phil] Yeah, tracks.

There's definitely something living down there.

-[Bruce] That's pretty neat. -Yeah.

It's really neat.

I mean, I'm surprised we haven't seen any fish.

It's almost like they're afraid of a giant robot

with lasers coming out of its face.

Lasers. Yeah. Yeah, yeah, that's a good point.

-[all laughing] -I would agree.

I'll tell you what, it is amazing to see the bottom of this lake.

I think we could safely say this ROV went

where no man or woman has gone before.

[Jessica] Yeah.

[Jessica] After another hour of searching,

whatever we saw on our sonar seems to have taken off.

[intense music playing]

We've been able to map out some of the bottom areas,

we've gotten a sense of where there's potential food,

where there's potential hiding spots.

[Jessica] The potential for something to be living in here, that's massive.

I mean, it has definitely enough space,

tons of food and very little interaction with people.

So if you're ever going to have a lake monster living anywhere,

I feel like this is the best place for that to happen.

And also, this is just one island

in the middle of a gigantic lake.

[Bruce] I think it'd take us a year

just to survey this little, this little tiny island.

Yeah.

[Josh] The deep waters of Iliamna Lake

in the sparsely populated wilds of Alaska

could indeed be the perfect place

for a large aquatic animal to remain undetected.

But is it really a legendary monster

or some known creature being mistaken for a monster?

Jess's kayak experiment to test

if the animal truly is drawn to the color red

yielded no alerts from the seismograph or camera trap.

And even though there are certain sharks that can inhabit fresh water,

so far none have been confirmed here.

Phil also considered the sturgeon.

They are a huge, prehistoric looking fish,

but they're also bottom feeders,

rarely seen at the surface,

and they're undocumented in lake waters this cold.

We analyzed the cell phone video captured by the Salmon sisters.

Even with digital enhancement, the visual here is a giant wake.

But there is no proof of what caused it.

So where does this leave us?

Phil suspects that in a place so steeped in native lore,

multiple sightings over decades of different aquatic species

that aren't known to be here may have combined to inspire a monster myth.

And after seeing firsthand, Iliamna's all-you-can-eat salmon special,

followed by a fast-moving shadow at the rocky overhang,

Jess is doubling down that there is something unclassified

growing large in the lake.

But what it is and where it came from is still a mystery.

Which brings us to this.

Remember those underwater cameras

Bruce and Mark have been placing throughout the lake?

The data is in and the results are, well, adorable.

This is an extremely rare and very cute freshwater seal.

Iliamna Lake is one of the few places in the world

that you'll find seals living in a freshwater habitat.

And just like a certain legendary lake monster,

there's a lot that scientists don't know about them,

like how they got here,

why they came and why they stay.

The Iliamna seals average just six feet long,

meaning they're probably not being mistaken for any monsters.

But if they can be in the lake unseen by most,

perhaps some other mysterious creature

might have found its way here

and could still be hiding in the depths.

For more information on Expedition X,

head to Discovery.com/ExpeditionX.