All language subtitles for What.on.Earth.S10E07.1080p.DSCP.WEB-DL.AAC2.0.H.264-BTN_track3_[eng]

NARRATOR:
They're watching you.

More than 5,000 satellites
circle the Earth.

Every day, they uncover
new, mysterious phenomena

that defy explanation.

Decoded from the skies.

The Roman chamber of secrets.

There are so many things that
we just don't understand.

NARRATOR:
The unstoppable toxic tsunami.

It's picking out any person
and anything in its way.

NARRATOR: And tomb
of Frankenstein.

KOUROUNIS:
We've got multiple bodies

brought together to create
these composite mummies.

NARRATOR: Baffling phenomena,
mysteries from space.

What on Earth are they?

[theme music playing]

Yorkshire, Northern England,

a region first
occupied 10,000 years ago,

a land of warring tribes,
Vikings, even vampires.

This area has a lot of history
attached to it.

Nearby is the town
of Whitby,

where Dracula supposedly
terrorized the population.

NARRATOR:
As well as bloody literature,

this county's history
is written

in the ruins littering
its landscape,

ones that can be
decoded from the skies,

including a site only
recently discovered.

There are so many
mysteries on this site.

There's just so many things
that we just don't understand.

NARRATOR: During construction
of a housing complex,

excavators have uncovered
a vast

array of structures lost
to history,

structures built, according to
lead archaeologist

Paula Ware, more than
1,500 years ago.

What we've actually got is

an incredibly sophisticated
complex of Roman buildings.

And they're the most
impressive that

I've ever seen in my career.

NARRATOR: Thousands of
Roman ruins litter

Europe and Britain, relics of
the greatest empire

of antiquity.

But there is no record
of these massive structures,

and their layout
is highly unusual.

This is a massive discovery,
and archaeologists

are even calling it
a world first.

HORTON: There's no parallel for
it anywhere else in the world,

and there's
no clear explanation

as to what its function was.

NARRATOR:
To solve the mystery,

Ware's team is turning
to the skies.

A drone captures hundreds of
aerial photographs.

These images are processed to
produce a detailed 3D model

of the structures.

WARE: The model that's being
produced is just amazing.

It's absolutely incredible in
giving us so much

detail that we can't even see
on the ground.

NARRATOR: The drone reveals
a sophisticated array of

buildings, likely built around
the 3rd century A.D.

The preservation is
quite remarkable.

But what were
these buildings used for?

We have no idea, and it's got
Roman specialists stumped.

NARRATOR: Historians turn
to the Romans'

conquest of Britain for clues,

a conquest that begins when
Julius Caesar invades

the island 55 years before
the birth of Christ.

It takes more than
a century of slaughter

and subjugation before Rome's
legions reach Yorkshire.

This part of North Yorkshire
was actually

at the extreme limit of
the Roman empire.

This is where Rome ended
and the wilderness,

from their perspective, began.

NARRATOR: The wilderness is
what we now call Scotland,

territory of
fearsome warriors,

the Picts.

The Picts are a mysterious set
of Scottish tribes.

They're known as
the painted people

because of their body art
and tattoos.

This was the only group of
people in this area who

were able to stand their
ground successfully against

the advancing Roman legions.

They must have been
quite astonishing.

NARRATOR:
The Picts' ferocity forces

the Romans to construct
a giant

barrier between their empire
and Scotland,

the 73-mile-long
Hadrian's Wall.

Over the following decades,
Rome launches

several attempts to subdue
the wild Scots.

This culminates in

a Roman invasion of
unparalleled brutality,

one that some speculate
could help explain

the ruins being studied
from the skies.

The site might be connected to
the emperor Septimus Severus,

who moved to this area of
North Yorkshire

for three years,
from A.D. 208 to 211.

He was annoyed that there was
this anomalous boundary at

Hadrian's Wall.

He wanted to capture
the whole of Scotland.

NARRATOR: To quash the Picts,
Severus unleashes the fury of

some 57,000 elite Roman troops.

Septimus Severus
planned a conquest of

extraordinary violence.

The Roman army basically
killed everything that was in

its way -- women, children,
dogs, cattle, sheep.

It was a very brutal campaign
into the heart of Scotland.

[man grunts]

SILBEY: But what he discovered
was that they were simply

too wild, too resistant to live
loyally as subjects of Rome.

So after signing the peace
treaty with the Scots,

Severus retreated back behind
Hadrian's Wall.

NARRATOR: Near the mystery
structures are the remains of

military camps used during
Rome's wars with the Picts.

But Ware doubts this complex
served a similar purpose.

At the present time,
we have absolutely no

evidence to support a military
occupation of this site.

It's the level
of sophistication

and detail that makes this
so different.

NARRATOR: Unlike military
fortifications,

some of the structures

here are formed from ornate
decorated limestone,

a sign that whoever once lived
here had amassed huge wealth.

The amount of capital
that's gone

into these buildings is
just incredible.

It would have been
a real showpiece.

NARRATOR: During the Romans'
occupation of England,

they create vast farms,
turning it into a grain basket

for the empire's
500,000 soldiers.

Landowners use their riches
to construct massive,

ornate villas,
which partially resemble

the mystery structures.

But key aspects differ.

WARE:
The villas that we have in

the area conform to standard
villa plans.

What we're looking at here
does not conform to

those plans, and that really is
the big mystery.

NARRATOR: The answer
to the riddle

could lie in the chambers
at the center of the complex.

Experts speculate their shape
and arrangement suggests

they were a place of
secretive rituals.

Roman temples will
often have a central tower,

a circular tower,
but the fact

it's got these projecting
wings is a completely

unique feature.

It's the three rooms
that have got most Roman

specialists intrigued as to
the function of these buildings.

One of the theories is
maybe we're

looking at some form of
cult activity.

NARRATOR: Rome was a hotbed of
religious cults,

and one infamous
for its gruesome practices is

known to have flourished near
the mystery structures.

Even the Romans, who would
gather in stadiums to watch

people fed to animals,
found this cult too barbaric

for them.

The question is, is the
structure associated with that?

NARRATOR: Coming up,
blood orgies of ancient Rome.

They would pass
their sexual powers over

to the goddess.

NARRATOR: And Hitler's
secret super gun.

We're talking about a gun
barrel the length

of the height of the Statue
of Liberty.

NARRATOR: In Yorkshire,
Northern England, archaeologist

Paula Ware is decoding newly
discovered ancient ruins.

What we've actually got is

an incredibly sophisticated
complex of Roman buildings.

NARRATOR: Aerial modeling
has revealed a strange

cross-shaped array of chambers,
possibly ritualistic,

but unlike anything
discovered before.

We don't know the actual
function of this complex

of buildings.

Are we looking at a religious
or cult site?

SILBEY: The Romans had
an enormous number of different

cults -- that would explain
why this is not

the kind of design
we've seen from any other

Roman architecture.

NARRATOR: Pagan Romans had 12
gods and goddesses, which

they believed ruled heaven,
the earth, and the underworld.

Yet as their empire grows,
some adopt new deities,

ones worshipped in secret,

away from the prying eyes
of religious authorities.

We tend to think of
the pantheon of Roman gods --

Jupiter, Juno, Mars, Venus --

being the only gods
Romans worshiped.

But that is entirely not
the case.

NARRATOR:
Followers of these new gods

formed so-called
mystery cults --

sects renowned for
their secrecy, symbols,

and harrowing
initiation ceremonies.

They attract landowners
and soldiers seeking good

fortune in times
of hardship and war.

The Roman army was notorious
for the variety

of cults that were followed
by the soldiers.

HUNT: One of the cults that
was extremely popular

with the Roman legions was
the cult of Mithras.

NARRATOR: Mithras, a god
believed to be able

to control the cosmos
and fight evil,

once rivaled Christianity
and popularity among Romans.

[animal groaning]

Cult members undergo
seven stages of initiation,

culminating in the ritual
slaughter of a bull.

[animal groaning loudly]

HUNT: The bull's blood was said
to balance out

good and evil, and if you
bathed in bull's blood,

your sins could be
washed away.

NARRATOR:
Mithras is known to have been

worshipped in Roman England.

However, another discovery in
Yorkshire could suggest these

chambers were used
by an even bloodier cult.

HYMEL: Nearby, archaeologists
discovered a skeleton

wearing a lot of jewelry.

So the archaeologists at first
believed that this was a woman

of power and authority in
the society,

but on further examination,
they realized it's a eunuch.

NARRATOR: The castrated cadaver
is believed to have been

a follower of Cybele,

a goddess of war and protector
against disease.

Her cult takes hold when
soldiers credit her powers

for their victory over General
Hannibal during the Punic Wars.

One of her functions was
the protector of cities,

the protector of walls,
and that's one of

the reasons Rome imported her
to protect their walls

against Hannibal.

NARRATOR: Cybele is also
a goddess of fertility,

and her followers worship her
with orgiastic abandon.

The priests had to castrate
themselves while in a state of

sexual arousal --
this was

particularly important so that
they would then pass

their sexual powers
over to the goddess.

They often
cut themselves a little

too badly and bled to death

right in the middle
of their frenzy.

NARRATOR: As the cult's members
swell in numbers,

its rituals draw the anger of
officials back in Rome.

There were so many families
who were deprived of sons

who essentially cut off
the lineage

and so much bloodletting
that the cult was

ultimately banned.

I don't know what
the punishment was for

worshiping,
but it couldn't be any worse

than what those priests
were doing to themselves.

NARRATOR:
Despite being forbidden,

the cult carries on in secret
for many decades

in far-flung
regions of the empire.

HUNT: Is this building

a worship site far on
the remote frontiers,

away from the watchful eye
of Rome?

NARRATOR: The mysteries
of this complex extend

beyond the strange chambers
at its center.

Around it, Ware
and her team have

found elaborate plunge pools
and heating systems,

but for some reason,
they were never used.

They've gone
to all the expense

of fitting them out,
and then suddenly,

it's abandoned.

Once the Romans
completed building it,

they just packed up
their bags and left.

Why would they do that?

WARE: Is it part of
a religious cult that

is no longer fashionable
and falls out of favor?

It's clearly a mystery.

NARRATOR: The strange
structures modeled from

the air continue to confound
experts on the ground.

WARE: The discovery of these
buildings is really making us

reassess our knowledge of
the Roman Empire in the north.

Whoever built it is not clear,

but it was clearly a site of
huge importance.

NARRATOR: Coming up,
jungle Armageddon.

Everything in its way was
literally wiped out.

NARRATOR:
And the tomb of horrors.

NELSON: They found bones
that were gnawed on,

which suggests
there was cannibalism.

NARRATOR:
January 2019.

A NASA Earth
observation satellite

scans the 225,000-square-mile
state

of Minas Gerais
in Southeastern Brazil

and captures an
unfolding disaster.

At one point, there was
villages and jungle,

but then in the next image,

there's this red smear
across the landscape.

HORTON: This is the most
eerie picture.

There's a great blob
of red, with tentacles

extending out into the valleys
on either side.

RUBEN:
This covers a massive area.

So whatever happened here,

it is tremendous in scale,
and it is not good.

NARRATOR:
The weird mass has engulfed

an area equivalent to
470 football fields.

Typically, when I've seen
images like this before,

it's been as a result of
a flood.

The thing is, there's no big
bodies of water here, no lakes,

no big rivers, and no evidence
of an extraordinary rainfall

that has recently come down.

And also, why is it red?

Analysts turned
to Maxar's SecureWatch

technology for answers.
-Looking at clues from

the satellite images,

there's a large open pit mine
right next to the disaster site.

And what it looks like
happened is

the dam that formed
the tailings pond

collapsed dramatically.

NARRATOR: Security footage
captures the 280-foot-high

tailing dam's
catastrophic collapse.

Three billion gallons of
noxious sludge,

a mix of mining waste, muck,

and mud, cascades
across the landscape.

It was like a tsunami,
and everything

in its wake was literally
wiped out.

NARRATOR: Moments later,
the giant, unstoppable wave

of muck sweeps into the mine.

It is now
around 40 feet high

and traveling
at 100 feet per second.

Security cameras have picked
up people running for

their lives,

cars being enveloped
in this wall of mud,

knowing that there will
actually be no escape.

NARRATOR:
The wall of death then flows

into the valley below,
engulfing entire communities.

RUBEN: It's taking out
cars, houses,

any person and anything in
its way.

KOUROUNIS: It basically
kills everything in its path

and leaves that area
pretty much

uninhabitable afterwards.

NARRATOR: Aerial images reveal
that within 10 minutes,

four billion cubic feet of
contaminated waste has swamped

the land and flowed into
nearby rivers.

The tragedy claims
more than 250 lives.

The aftermath is
absolutely apocalyptic --

rescue workers digging through

this toxic mud, trying to find
any sign of survivors.

There were still people
unaccounted for.

So probably,
we will never know

the exact number
killed in this disaster.

NARRATOR: Authorities
deployed 2,500 people to

help with cleanup
and rescue operations,

painstakingly searching through
mud up to 45 feet thick.

With bereaved families
demanding answers,

investigators turn
their attention to

the cause of the dam's sudden
calamitous failure.

This type of dam failure
is particularly

awful in that there were
no foreboding signs.

There's no slow-moving
destruction that

you can watch and prepare for.

It happens all at once.

NARRATOR: This mine,
called Corrego do Feijao,

is one of over
300 in Brazil.

Together,
they produce more than 450

million tons of iron ore
a year,

enough to build 3,000
Golden Gate Bridges.

At the site in the image,
waste from the extraction

process is pumped into a walled
pond higher up the valley.

The method is what's known as
upstream tailing,

which effectively means you
use the tailings themselves

to create the dam.

The tailings are kind of
piled on top of each other

in a way that they deform
and harden to make the wall.

NARRATOR: Authorities discover
that the tailings dam

suffered from several
design defects,

including poor water
management and drainage.

Once it became
too saturated and unstable,

all hell broke loose.

KOUROUNIS: Hundreds of people
died in this disaster

that could have been
absolutely prevented

had the dam been designed
properly in the first place.

NARRATOR: What's more, analysts
learn that six similar dams

in Brazil have failed in
the past few years.

And the situation
is getting worse.

What's really scary
is that this flawed

type of construction is not
limited to Brazil.

So it's entirely possible
to see one of

these dam failures happen
a lot closer to home.

RUBEN:
This was horrible and tragic.

But there are dams
like this all around

the world, and the same thing
could happen to them.

NARRATOR: In the U.S. alone,
over 40 such dams

are considered high risk.

It fuels fears
that this will not be

the last time such devastation
is captured from the skies.

And it's not just the short-term
disastrous effects.

There's also the long-term
ecological effects

of this toxic sludge

that will be around for
decades or maybe even

generations to come.

NARRATOR: Coming up,
the mysterious curse of

the Kennedys.

What we're seeing here changed
the course of history itself.

NARRATOR:
And lair of the bog bodies.

We're looking at a real-life
Frankenstein here.

NARRATOR: Spring 2021.

Aerial archaeologists take to
the skies over Northern Poland.

On-board lasers pierce
the forest canopy below,

peeling back history,

and capture a puzzle
hidden from human eyes.

It looks like
something dragged

massive claws
through the forest.

They're long.
They're hundreds of feet long.

I don't know what caused this,

but it's very strange,
very unusual.

NARRATOR: For centuries,

locals here have reported
sightings of

a monstrous clawed creature
called a basilisk.

Further aerial images suggest
the giant gashes in

the woods may have a similarly
disturbing origin.

These slashes in the forest
actually remind me of

something else
I've seen in Poland,

and that's long barrows,
which are elongated tombs.

NARRATOR: Like the structures
in the image,

the tombs are around
350 feet in length

and perfectly straight.

They are the resting place of
people buried 5,000 years ago,

long before the construction
of the great pyramids of Giza.

But it's not just the age of
the cadavers discovered here

that intrigues experts.

NELSON: At one particular site,

they found bones that were not
only charred, but gnawed on,

which suggests there
was cannibalism.

HUNT:
But this doesn't appear to

be haphazard cannibalism
from starvation.

They're doing it ritually.

NARRATOR: Analysis
suggests the tombs were

the site of some kind of
cannibal feast,

where bones were cooked
and broken

to consume the marrow
concealed inside.

Often, cannibalism is
a reflection of people

who want the power of
their predecessors.

So if you have a chieftain

who is a mighty warrior,

if you eat part
of that chieftain,

you assimilate that power.

Maybe what
we're looking at here

are three long parallel tombs.

NARRATOR: Military historian
Martin Morgan disagrees.

He's convinced the mystery
structures are

the hidden remains of
a cataclysmic weapon,

one that threatened to
change the course of history.

MORGAN: There's nothing like it
anywhere else on Earth.

We're talking about
a gun barrel

the length of the height of
the Statue of Liberty.

NARRATOR: The story of
the massive super gun

begins in 1943.

In retaliation for
devastating Allied

bombing campaigns,

Nazi Minister of War
Albert Speer announces

the development of a series of
so-called vengeance weapons.

The idea of these vengeance
weapons was to chip away at

the morale of the people that
were on the receiving end of

the attack,

that they would eventually
become so dispirited,

that they wouldn't want to
fight any longer.

In June 1944,
German scientists in Poland

unleashed the V-1,

a flying bomb armed with
a 2,000-pound warhead.

This is quickly followed
by the V-2,

the first ballistic missile
in history.

And the Nazis
are just warming up.

What we're seeing are
the remains of

the test platforms
for the V-3.

The V-3 super gun was
the most awesome of them all.

NARRATOR: The V-3 is the biggest
gun the world had ever seen.

Over 400 feet long,

the massive cannon can propel
a 310-pound shell

more than 100 miles.

MORGAN:
You can't aim this gun barrel.

Cannoneers had to compensate
for the rotation of

the Earth
when they were firing

over such a great distance.

It's pretty amazing to think
about the size of

that gun, that it required
an entire hillside for support.

NARRATOR: After secret
tests at the site

in the image,
Hitler begins construction

of a V-3 battery in
northern France.

His plan is to install
25 super guns,

each unleashing one bomb
every 12 seconds

over the English Channel
and on to London.

It's terrifying to think about
that as

a possibility --
the blitz was bad enough.

This would be worse.

This would have devastated
England, and it

would have turned the tide of
the war.

NARRATOR: When Allied
intelligence officers learn

of Hitler's new mega weapon,

they initiate a plan to
destroy the French bunkers,

code-named Project Anvil.

The idea was, essentially, that
they would pack a plane full of

bombs and then remotely
crash into the bunker

and take care of business.

It had to take off
with pilots aboard.

Then these two pilots would
bail out of the aircraft, and it

would continue on under remote
control all the way to

the target.

NARRATOR: The man charged with
piloting the flying bomb

is Joseph Kennedy, Jr.,
brother to the future

U.S. President.

20 minutes after
he begins the mission,

disaster strikes.

Something went wrong --
as they armed the explosives,

the entire package exploded,

killing both men inside
the aircraft even before it flew

out over the English Channel.

Adding to the tragedy is that

it could have been
avoided completely.

MORGAN: Unknown to Project Anvil
and the people working in it,

the RAF dropped a series
of Tallboy bombs

that destroyed the site

to the extent that it
could not be used.

NARRATOR: In honor of
Joseph Kennedy,

the U.S. Navy names
a destroyer after him,

on which his brother serves.

75 years later,

the test site that led to his
death and threatened to kill

millions of others is
revealed from the skies.

CHAMBERLAIN: What we're
seeing here are the remnants

of a Nazi weapon
that could have

changed the course of
history itself.

NARRATOR: Coming up --
the human jigsaw.

JANULIS: Somebody has gone
through bones from different

people, putting them together
into one composite body.

And attack of
the 5,000-mile-long blob.

Is it something alive?

Is it a lot of
somethings alive?

NARRATOR:
May 5th, 2017.

A satellite scan
the Outer Hebrides,

off the northwestern
coast of great Britain.

In this image, we're seeing
what looks to be some strange

structure on the island
of North Uist,

off the coast of Scotland.

KAYS: It's not clear exactly
what kind of structure it is,

but it is striking in that it
is in the middle of what's

otherwise just very sort of
barren-looking land.

NARRATOR:
Drone footage reveals further

details about
the mystery structure.

KAYS: You can see that this is
actually pretty big.

It's about 80 feet wide.

And it looks like,
from this angle,

it's basically
a giant mound of rocks.

KOUROUNIS: To me, this looks
a bit like a burial mound,

and there might be some type
of an actual entrance.

NARRATOR: The satellite image
has captured a chambered cairn,

a kind of tomb built thousands
of years ago.

Its scale and remote location
intrigue archaeologists.

HUNT: Its size

could suggest that it's
the burial site

of a very important person

who is surrounded by a pretty
big array of grave goods.

NARRATOR:
Excavations on burial sites

on a neighboring island
could shed light

on who is
interred in the massive tomb.

What we found were skeletons

that were incredibly
well preserved.

But there was something
a little bit strange

about those skeletons.

YORK: It appears that they had
been preserved in some kind of

an acidic condition,
likely a peat bog.

NARRATOR:
The cadavers are examples

of what are known as bog bodies,

corpses preserved
for millennia

after falling into
peat marshes.

JANULIS: Peat bogs are very
dense, they're very low oxygen,

and they have a lot of acid.

So what that means is if
a body falls into a peat bog,

it might be found thousands of
years later in a relatively

intact condition.

NARRATOR: Weirder still,
these corpses had been

intentionally submerged
in the bog and then exhumed,

the first examples of

deliberate mummification
discovered in Europe.

To add another layer
of strangeness

to this whole thing,

research reveals somebody has
gone through carefully, taking

bones from different people

and putting them together
into one composite body.

We're looking at a real-life
Frankenstein here.

NARRATOR:
The bodies found near the tomb

in the image
are Bronze Age chimeras,

Franken-mummies

fashioned from several
different generations

of ancestors.

Further radiocarbon
examination shows that these

actual bones span
hundreds of years.

We've got multiple bodies
brought together over who knows

what period of time to create
these composite mummies.

JANULIS:
These were found not very far

from where our image sits.

So is it possible that our

structure has a Franken-mummy
inside it?

NARRATOR: Yet when experts turn
to the archaeological record,

the mystery deepens.

YORK: The structure that we're
seeing in these images is

actually thousands of years
older than these mummies.

It was likely built by
their ancestors.

NARRATOR: The tomb appears
to have been constructed during

an intriguing period in human
evolution -- the Neolithic.

This is a time when mankind
move from hunting

and gathering to a life of
agriculture and settlement.

Giant mysterious
stone structures also

begin appearing across
the land.

CAVELL: All over, there are
Neolithic sites that

ancient Britons constructed as
temples or observatories.

NELSON: We know very little
about Neolithic structures

but the ones that exist

today seem to be used for some
sort of religious

or ceremonial purpose.

NARRATOR: Scotland's islands
are among the first places

to witness the arrival of
these strange monuments,

coded legacies of
history's first

true civilizations
wrought in stone.

CAVELL: Some of
these settlements go back

to 3,000 B.C.E.,

and clearly,
it's been a place

of great importance for a lot
of those ancient people,

because there are
so many of these

stone circles
and ritual sites.

NARRATOR: The giant tomb
revealed from the skies

may have been built to honor

one of the leaders of
these ancient peoples

who transformed the world.

But with much of it
now collapsed,

their identity will likely
remain a mystery.

This is a really enigmatic
monument, attesting to

the longevity of their culture
in such a barren,

remote place.

NARRATOR: Coming up,
the 22-million-ton sea monster.

Once it starts hitting
the shoreline, that's

when all the problems really
start to begin.

NARRATOR:
June 26th, 2018.

Satellites capture
something massive

lurking off the Florida coast.

There's something unusual
going on in the Atlantic.

There's some orange-brownish

substance that's enveloping
the coastline.

It looks like the whole
coastline is full of goo.

RUBEN:
Whatever this substance is,

there's just tons
and tons of it.

Is it something that spilled?

Is it something alive?

Is it a lot of
somethings alive?

NARRATOR: Additional satellite
data reveals something bizarre,

blobs of the mystery goop span
more than 5,000 miles of ocean.

This is not just some
local phenomenon.

This thing is
stretching across

the Atlantic Ocean, like
literally all the way.

KOUROUNIS: From the west coast
of Africa to Florida,

it's just one big
mass of orange.

NARRATOR: Analysts track
the weird mass to its source.

This thing seems
to be coming from

a part of the Atlantic called
the Sargasso Sea.

And the Sargasso Sea
is named after sargassum.

I think maybe that's
what we're seeing here.

NARRATOR: Sargassum is a type of
floating seaweed

carried over vast distances
by the ocean currents.

Freak conditions have created

the biggest bloom of it
on record --

22 million tons,

equivalent to more than 200
fully loaded aircraft carriers.

We think of sea monsters
as being

these animals coming up from
the depths.

But in this particular case,
our sea monster is a plant

that has grown to the point

where it's taking over
an ocean.

Even though this sargassum bloom
happens every single year,

we had never seen it
at this size before.

NARRATOR:
In the vast open ocean,

the seaweed islands
provide food, shelter,

and breeding grounds
for a host of animals.

When they head towards land
in big numbers,

it's a whole other story.

It's one thing to have all
this seaweed far out to sea,

but once it starts hitting
the shoreline,

that's when all the problems
really start.

NARRATOR:
Seaweed tsunamis 30 feet deep

strip the ocean of oxygen,

block out sunlight,
and turn the entire coast

into a dead zone.

A little bit of sargassum
is normal and healthy,

but sargassum on this scale can
smother and suffocate corals

and sea grasses and lead to

the declining of
fish population.

NARRATOR: What's more,

alien species can use the mats

as mother ships to invade
Florida's waters.

Organisms and other animals
can ride on these

rafts of seaweed, traveling
from one place to another,

which unleashes a whole other
environmental problem.

NARRATOR: Waves and tides force
the sargassum onto beaches,

creating slimy mounds
stretching along hundreds of

miles of coastline,

and the sweet tropical air
soon turns fetid with

the scent of millions of tons
of rotting seaweed.

When this sargassum actually
starts to decompose,

the bacteria release
hydrogen sulfide.

So basically,
it smells like rotten eggs.

Hydrogen sulfide doesn't just
smell bad.

It's also been linked
to neurological,

digestive, and respiratory
symptoms in humans.

NARRATOR: Across Florida
and the Caribbean,

authorities spend tens of
millions of dollars

and deploy hundreds of
machines to clean up the mess.

It's possible
to clean up this algae,

but it's not easy,
and it's expensive.

You basically load it onto
trucks and drive it away,

and then after the truck is
gone, more of it washes up.

It's like that endless loop of
Sisyphus pushing that rock up

the hill, only to have it
tumble back down again

over and over
and over again.

NARRATOR: Scientists fear
this won't be the last time

this mega weed plagues
our shores,

creating the putrid waters and
beaches revealed from space.

These blooms have gotten
bigger and bigger for

the past decade, and there's
no sign of it slowing down.

FANARA: Deforestation,
use of fertilizer,

and changes in climate are

causing algae blooms
to occur more frequently

and more intensely.

This is something that can
happen over and over again,

and this may be our future.