♪ ♪ NARRATOR: Venice, Italy, is in peril.

MAN (speaking Italian): NARRATOR: The sea level rising.

♪ ♪ Extreme floods inundating the city.

♪ ♪ ROSA SALZBERG: It's really alarming to see what happens to Venice when it floods.

NARRATOR: The city itself crumbling.

Salt is the enemy of Venice.

NARRATOR: There may not be much time left to act.

GEORG UMGIESSER: There's a lot of responsibility on us.

Because if you make it wrong, people will feel it.

NARRATOR: Scientists and engineers are deploying new solutions to defend against the rising water.

From allying with nature... GIOVANNI CECCONI: This is the brick of life, the mud.

DAVIDE SERNAGLIA (speaking Italian): NARRATOR: ...to a multibillion-dollar flood defense system.

♪ ♪ A moonshot to save Venice from the next inundation.

Can they succeed and protect this ancient city?

♪ ♪ "Saving Venice."

Right now, on "NOVA."

♪ ♪ ♪ ♪ NARRATOR: Venice, Italy, an ancient city of tradition, arts, and culture.

♪ ♪ Home to iconic sights, like the Rialto Bridge, the Doge's Palace, and the Basilica San Marco.

♪ ♪ But it is perhaps most famous as the city of water, where people and goods travel by gondolas and boats along a network of canals.

♪ ♪ These waterways connect the city to a shallow, 210-square-mile tidal lagoon, separated from the Adriatic Sea by a string of spits and barrier islands that shelter this natural harbor.

Only at narrow inlets can ships pass in and out of the lagoon.

Over the centuries, the Venetians reinforced these natural barriers with sea walls and jetties.

But in the era of climate change, these defenses are no longer enough.

MAN (speaking Italian): NARRATOR: Venice experiences sudden floods, known as acqua alta, caused by the sea surging through the inlets.

♪ ♪ These can inundate over 80% of the city in a matter of hours and leave the lowest-lying areas under more than three feet of seawater.

In the entire 20th century, there were only nine of these extreme floods.

In just the first two decades of the 21st century, there were 16.

Venice is facing the reality of climate change.

MAN (speaking Italian): NARRATOR: A stark warning of what may be to come for other coastal cities.

ED BLAKELY: Over a hundred of our largest cities are built on coastlines.

40% of the world's population is on those coastlines.

So Venice is kind of the canary in this coal mine.

As Venice floods, undergoes these changes, all the world's cities can see what's going to happen to them.

♪ ♪ NARRATOR: Now the eyes of the world are watching as Venice puts a new flood barrier to the test.

SERNAGLIA (speaking Italian): NARRATOR: A multibillion-dollar system of gates designed to protect the city when the next flood threatens.

♪ ♪ SERNAGLIA: NARRATOR: But this barrier system is just the latest in a long line of Venetian engineering solutions.

♪ ♪ Living on a lagoon has posed problems since the first settlers arrived 1,600 years ago.

(bells ringing) The city of Venice wasn't the original settlement.

♪ ♪ Six miles northeast of the city, the first homes were built on the island of Torcello.

It is an area dominated by a network of shallow tidal creeks and low-lying salt marsh islands, which offered food and shelter to the first settlers.

♪ ♪ (speaking softly) ALBERTO BARAUSSE: Venice was born in the lagoon because the lagoon was useful to Venice.

So Venetians shaped the lagoon the way they wanted.

NARRATOR: But this environment posed a problem.

How could they build on such soft ground?

This is actually the, the kind of landscape they, they saw back then.

Uh, so very low-lying land, marshes, some islands, but in general very wet, swampy soil, such as this one.

I just want to show you how soft this mud is by trying and walk here.

I'm not that heavy weight.

I weigh 65 kilos.

But I'm sinking like this.

NARRATOR: 65 kilos is around 140 pounds.

If the mud can't support this, how could it bear the weight of a wooden house, let alone one of Venice's grand stone buildings?

♪ ♪ The solution?

Forcing wooden poles into the soft mud.

These poles don't support the weight.

(speaking Italian): NARRATOR: They transform the mud around them.

The idea is to do a little experiment.

When you plant many poles, they compact the mud between them.

The water is pushed out, and the compaction of the mud itself make the mud more capable of supporting weight.

NARRATOR: Modern-day excavations under the city reveal that Venetians maximized the compaction of the mud by using a large number of poles packed tightly together.

Directly on top, they placed wooden planks, then impermeable limestone.

And, above the waterline, bricks.

BARAUSSE (speaking Italian): There you see, I'm lightweight, more than him.

He can also try.

Okay, you see Omar is not sinking, because the effect of the poles that compacts the mud between them.

So it changes from more, I would say, fluid-like to more solid-like.

And the proof of this is when we put the plank over there and do the same thing on the mud without the poles underneath, you see?

There's a difference.

♪ ♪ NARRATOR: This technology is the secret of Venice's construction and longevity.

It allowed the first settlers to adapt the environment and build the first houses.

The Venetians used wooden piles to build on a cluster of 118 marshy islands.

And over the centuries, they created the city we see today.

BARAUSSE: Venice is standing on mud, it was built on mud, and it will stand for many, many years onwards.

NARRATOR: But building on low-lying islands does have a drawback.

♪ ♪ Venice sits barely above the level of the waves, and this has always made the city vulnerable.

SALZBERG: Marin Sanudo was a Venetian nobleman who, for about the first three decades of the 16th century, kept an almost daily diary of all kinds of things that were happening in the city.

So it's a kind of gold mine for Venetian historians.

NARRATOR: On November 16, 1517, he noted an event in the lowest part of Venice, the historic Piazza San Marco.

SALZBERG: He writes that "on Monday morning, "as it had rained a lot, both during the night "and in the morning, the water rose very much.

"So much so that St. Mark's Square, "from the Grand Canal to the Rialto, "and all the streets were full of water.

"And it was neither possible to travel "nor by land nor with boats.

"And it was terrible to see the water, which also "continued to rise.

"So much so that nobody remembers anything similar.

"It destroyed many goods in the shops, "and in many poor houses on the ground floor, it flooded all they had, causing them great hardship."

It's an extraordinary passage to read now, because it's, it's very evocative of what it's like, it's like to be in the city when there's an acqua alta, when there's a high water.

NARRATOR: For hundreds of years, floods have swept through the city.

And the cumulative effect of these inundations is placing the survival of Venice's buildings in doubt.

ELISABETTA ZENDRI (speaking Italian): NARRATOR: Scientists led by Elisabetta Zendri are monitoring the damage these floods inflict on the city.

♪ ♪ Venice is known as the city of canals.

And most of the historical buildings are in direct contact with seawater.

♪ ♪ The building materials are porous.

And seawater rises up the walls.

But this is not only water, this is salty water.

And when the water evaporates from the walls, the salt, uh, can crystallize into the pores.

♪ ♪ The crystallization pressure causes cracks of the pores.

And this is the final consequence.

All the façade is compromised.

This problem is present in all the buildings in the city.

Salt is the enemy of Venice.

NARRATOR: As climate change raises sea level, flooding is increasing.

More salt is getting into the porous brickwork.

And the problem is only going to get worse.

Models suggest the sea level here could rise more than 40 inches by the end of the century.

It would seem the future of this remarkable city is bleak.

But now there is hope.

♪ ♪ After nearly 20 years of construction and some $8 billion, a network of enormous flood barriers, called the MOSE, is in place.

It is designed to block the floodwaters before they reach the city.

In charge is Elisabetta Spitz.

♪ ♪ SPITZ (translated): The MOSE is a masterpiece of Italian engineering.

It has required so much labor, so much research, so much testing.

NARRATOR: The scale of this project is immense.

78 individual gates are arranged in four barriers that each stretch over 1,100 feet across the inlets to the lagoon.

At Chioggia, Malamocco, and two barriers separated by an artificial island at Lido, the widest entrance.

(ship horn blows) These inlets are the only way for commercial ships to access the lagoon.

♪ ♪ So the barriers are only lifted when a flood endangers Venice.

Each gate is colossal, approximately the size of two tennis courts.

(translated): These gates are fixed to concrete beds sitting on the bottom of the sea.

NARRATOR: During construction, each gate was connected to these beds by two immense hinges, which allow them to pivot.

The gates are full of water, which weighs them down and keeps them lying flat on the sea floor.

Until the team injects compressed air through a system of valves.

SPITZ (translated): Air is pumped into the gates, and they slowly rise.

And emerge from the sea.

Then they join together, and hold back the high tide.

NARRATOR: Most floods last fewer than four hours.

So once the threat has passed, the team can lower the barriers.

The MOSE is still in its testing phase.

The team is perfecting how to operate the barriers when an acqua alta threatens the city.

SPITZ (translated): This project needs to work perfectly.

Water cannot pass through.

(crowd cheering and applauding) NARRATOR: But deploying the barriers is far from straightforward.

An acqua alta arrives incredibly quickly.

The water can rise as much as 12 inches in just one hour.

And it takes over an hour to raise all the gates.

♪ ♪ Venice needs an early warning system that predicts exactly when the floods will arrive.

One factor is easy to forecast-- the tides.

The highest tides occur when the sun and the moon align, and their gravitational pull on the Earth's water combines.

Known as spring tides, they happen twice a month, and their timings can be calculated years in advance.

But Venice doesn't flood whenever there is a spring tide.

Another factor must combine with the high water to cause these inundations.

Understanding this is the key to predicting an acqua alta.

It is an issue that oceanographer Georg Umgiesser has been studying for almost 40 years.

UMGIESSER: Venice is a special city.

We have to protect it, because otherwise, generations will lose their history.

NARRATOR: To investigate, he ventures far beyond the city limits.

UMGIESSER: It's a special environment.

It's just out of the world.

NARRATOR: Georg's destination is a scientific monitoring platform.

UMGIESSER: I like to go out there.

It's very beautiful.

♪ ♪ NARRATOR: Ten miles from Venice, the monitoring platform sits in a strategic position at the northern end of the Adriatic Sea, a branch of the Mediterranean.

Here it detects any changes in sea conditions heading up this narrow body of water before they reach Venice.

♪ ♪ Measurements from the platform, along with data from across the Mediterranean, show that most of Venice's acqua alta have something in common.

A specific type of storm system in the Mediterranean.

When you have a low-pressure system, then you always have a wind circulation which is anti-clockwise.

The closer you get to the low-pressure system, the stronger the winds are.

And so once this is moving now closer to, to Italy, the winds also in the Adriatic Sea get stronger and stronger.

NARRATOR: Known as the sirocco, these winds are a major threat to Venice.

♪ ♪ UMGIESSER: Basically, they push the water against the northern part, and they push the water against the lagoon.

Then you have, also, the atmospheric pressure.

If you have lower pressure, the water raises up.

♪ ♪ NARRATOR: The twin effects of low pressure and wind can dramatically increase the water level in Venice.

And if these coincide with a spring tide, an acqua alta can hit.

♪ ♪ This combination is known as a surge tide.

As weather patterns change around the planet, the storm systems that drive these inundations have become more frequent.

♪ ♪ UMGIESSER: Exceptional high tides in Venice are classified as water level higher than 140 centimeters.

We saw in the last 150 years 18 events.

In the last three years, we saw seven.

So something is changing, clearly.

And the only reason why that could be is climate change.

♪ ♪ NARRATOR: But now Georg has an early warning system.

♪ ♪ If a spring tide is due, and a low-pressure system is forming, Georg will see changes in the water level at the platform up to a week before the surge tide arrives, giving him a way to alert Venice that a flood is on the way.

UMGIESSER: There's a lot of responsibility on us.

It's a burden, it's a burden, because if, if you make it wrong, uh, people will feel it.

NARRATOR: Georg has detected that water around the platform is rising.

This is a forecast we issued at the 30th of October.

Based on what we have here, we can see that at a certain point, just before the second of November, we should expect an event.

We are sure that something will happen here.

♪ ♪ NARRATOR: Georg is forecasting that at 8:45 p.m., a flood will hit the city that could cover the lowest-lying areas in almost 20 inches of seawater.

♪ ♪ At the MOSE, Davide Sernaglia is in charge of raising the barriers.

SERNAGLIA: We have 70 guys that work together here.

MARCELLO (speaking Italian): SERNAGLIA (speaking English): And all have to work like an orchestra.

♪ ♪ (speaking Italian): (speaking English): We have to check the compressor, the valve, the transmission system.

It's not possible to lost time.

But it's not simple.

(chuckles) NARRATOR: It's 7:45 a.m., and in the city, workers are inserting a backup plan in case the MOSE fails to lift.

MAURIZIO SCARPA (translated): We're positioning the raised walkways for the high-water event.

Tonight, this will all be flooded.

If the MOSE isn't put up, it will be flooded.

♪ ♪ They say it will be raised up, but we can't say for certain.

♪ ♪ NARRATOR: The approaching flood is predicted to inundate nearly half the city.

♪ ♪ Kiosk owner Walter Mutti remembers the havoc when an acqua alta hit on November 12, 2019.

(water splashing) MUTTI (translated): At 9:30, suddenly the wind changed.

(sirens blaring) The flood sirens began to sound.

The wind suddenly became merciless, extremely strong.

The tide was increasing out of all proportion.

In 20 minutes, it had grown by eight to 12 inches, which is unheard of.

I was inside and I felt the newsstand shaking.

I came out and the water was already this high.

I went home, and when I came back at 2:00 a.m. to try and save the papers and so on, I couldn't see my kiosk anymore.

NARRATOR: Walter had to wait three weeks before he could solve the mystery of what had happened to his kiosk.

MUTTI: The fire department came and they searched the canal.

They found a newsstand, but it was full of mud.

I understood that I lost everything.

♪ ♪ NARRATOR: It cost $30,000 to restore his kiosk.

And Walter knows another flood could spell financial ruin.

MUTTI: I hope it never happens again.

I hope my fears are not realized and that the MOSE will work.

♪ ♪ NARRATOR: It's 5:45 p.m. Davide and his team need to raise all the gates before the surge tide arrives in three hours.

♪ ♪ But there is bad news.

SERNAGLIA (speaking Italian): ♪ ♪ NARRATOR: The wind has changed direction, pushing the storm towards Venice and causing the tide to rise far faster than expected.

SERNAGLIA: NARRATOR: Davide orders the immediate lifting of Treporti, the northernmost set of gates.

SERNAGLIA: MARCELLO (speaking Italian): SERNAGLIA: MARCELLO: SERNAGLIA: ♪ ♪ MARCELLO: ♪ ♪ NARRATOR: But outside, the storm intensifies.

(wind roaring) MARCELLO: SERNAGLIA: ♪ ♪ NARRATOR: With all the Treporti gates safely deployed, Davide orders the lifting of the other barriers.

SERNAGLIA: ♪ ♪ NARRATOR: But two of the San Nicolò gates aren't rising.

SERNAGLIA: NARRATOR: Each gate has safety valves to prevent it from accidentally rising up.

They have to be open to allow air into the gate.

Otherwise, it won't lift.

SERNAGLIA: MAN (on radio, speaking Italian): SERNAGLIA: ♪ ♪ NARRATOR: Davide suspects that the safety valves haven't opened on these two gates, and they can't rise into position.

And the storm is driving the water over three inches higher than expected.

SERNAGLIA: STEFANO (speaking Italian): ♪ ♪ NARRATOR: Davide decides the only option is to risk rebooting the system.

SERNAGLIA: ♪ ♪ FRANCESCO (speaking Italian): SERNAGLIA: (man speaks on radio) ♪ ♪ FRANCESCO: MAN (on radio, speaking Italian): SERNAGLIA: MAN (on radio): SERNAGLIA: SERNAGLIA: ♪ ♪ NARRATOR: The lowest parts of Venice had been forecast to be under almost 20 inches of damaging seawater.

But in the Piazza San Marco, the only water is rain.

(people talking and laughing) The MOSE has kept the acqua alta out of Venice.

SERNAGLIA (speaking Italian): ♪ ♪ NARRATOR: The following morning, one Venetian in particular is feeling positive.

(humming) MUTTI (translated): In the end, everything was fine.

Luckily, they lifted the MOSE.

And so personally, I, like the rest of the city, breathe a sigh of relief.

It gives you more faith, definitely.

(chuckles): However, tomorrow is another battle.

(bell tolls) NARRATOR: Just 36 hours later, Walter is proved right.

♪ ♪ The Piazza San Marco is flooding.

♪ ♪ A surge tide is forcing seawater up through the drains, and a torrent is pouring into the basilica.

♪ ♪ Inside, seawater is coming up through the floor.

(water gurgling) The reason is, three miles away, the MOSE hasn't been deployed.

This isn't because of mechanical failure.

For now, the barriers are only raised for the most extreme high waters.

♪ ♪ But smaller acqua alta aren't blocked and can still inundate the lowest-lying parts of the city.

♪ ♪ There is a good explanation for this decision.

Raising the flood barriers too often also poses a threat to the city and its people.

♪ ♪ Giovanni Cecconi has studied the lagoon for over 40 years.

Including almost 20 years working on the MOSE.

♪ ♪ CECCONI: If we stop the tide, if we use the MOSE too much, then the lagoon will die.

A healthy lagoon make the Venice city healthier.

♪ ♪ NARRATOR: And the key to a healthy lagoon is the tide.

CECCONI: Twice a day, we have a cycle of inflow and outflow.

Because of the tide, this water is mixed.

If you don't have the stirring, the same old water will get more and more polluted.

NARRATOR: And Venetians rely on the lagoon's tides for one of the most basic pieces of the city's infrastructure.

CECCONI: In Venice, you don't have a septic sewage system.

So the waste is discharged into the inner canal.

♪ ♪ NARRATOR: When the MOSE is closed, there is no tide, and human waste accumulates.

♪ ♪ CECCONI: It is very important that the sewage system is flushed by the tide.

♪ ♪ Because without the tide, the, Venice will die in its own, uh, waste.

(chuckles) NARRATOR: Because of climate change, Venice will need to deploy the MOSE more and more often.

But doing so will jeopardize the city and its people.

♪ ♪ Scientists need to find more ways to protect Venice that work alongside the MOSE.

And the answer could be hiding in plain sight: the salt marshes.

This network of islands acts as a natural flood barrier, channeling water and reducing the power of waves.

And salt marshes have another advantage.

They can keep pace with sea level rise because of the way that they grow.

♪ ♪ These two plants are cooperating to keep the soil higher.

The roots are very important because they hold the soil together.

At the same time, they push the plant a little higher.

This is the first mechanism of counteracting sea level rise, producing more volume below.

♪ ♪ NARRATOR: In summer, these plants grow rapidly, forming a thick carpet of vegetation.

As high tides flow over the salt marsh, this web of branches and stems acts like a giant fishing net, trapping mud and debris that then settle on top of the salt marsh, causing it to gain height and providing a mechanism for the marshes to keep pace with sea level rise.

CECCONI: The more it is flooded, the more it grows.

Each year, it is growing now more than one or two centimeter.

♪ ♪ NARRATOR: These low-lying marshes have yet another benefit.

They offer one of the most potent ways of fighting climate change on the planet.

♪ ♪ Acre for acre, they can lock up carbon 50 times faster than the Amazon rain forest.

♪ ♪ But in Venice's lagoon, salt marshes are in decline.

200 years ago, there were nearly 70 square miles.

Now there are just 16.

♪ ♪ This decrease is linked largely to one factor: erosion from ships.

All cargo ships access the lagoon via the Malamocco Inlet.

They follow a narrow channel to reach Porto Marghera.

♪ ♪ Just two miles from Venice, this is one of the busiest ports in Italy, processing over 25 million tons of cargo every year.

♪ ♪ Coastal researcher Luca Zaggia is worried the city and its lagoon are at risk from all these large cargo vessels.

♪ ♪ ZAGGIA: The ships are getting bigger.

So starting from the '60s, they doubled the size.

Today, we have ships as long as 300 meters, which is, uh, quite a lot for this channel.

NARRATOR: 300 meters is the length of six Olympic-size swimming pools-- nearly 1,000 feet.

And when it comes to ships, size matters.

♪ ♪ ZAGGIA: This is a big wake.

Well, that was not bad.

So now, on the, on the side, you see the water bounces back and forth for about 15, 20 minutes.

And the erosion created by the ships, it's undercutting the shore.

And we lost here essentially 150 meters.

♪ ♪ NARRATOR: The larger the ship and the quicker it is moving, the faster the erosion due to the size of the waves.

ZAGGIA (speaking Italian): NARRATOR: A ship's momentum generates two different destructive waves.

ZAGGIA: NARRATOR: First, a depression wave that sucks water towards the vessel.

ZAGGIA: NARRATOR: And then a displacement wave generated by the hull, pushing water out of the way as the vessel powers forward.

♪ ♪ The power of these two waves combines to destroy the land close to the channel.

The ship wakes, they arrive until this point.

They undercut the cliff.

And finally, slabs of soil will collapse.

Over a year, you can lose about four meters of shoreline.

♪ ♪ NARRATOR: And on the other side of the channel, the waves from large ships are scouring mud from the sea floor.

Since the 1970s, erosion has caused the lagoon to become over three feet deeper.

♪ ♪ And when the lagoon gets deeper, it increases the risk of Venice flooding.

ZAGGIA: This is a buffer between the land and the ocean.

You have no idea of how many problems you can have on the coast without this buffer.

So we need to limit the erosion if we want to save Venice.

NARRATOR: But that's becoming more difficult.

Traffic in this channel is increasing.

(ship horn blows) Cruise ships used to sail right through the center of Venice.

Here, they traveled very slowly and produced only very small wakes.

(ship horn blaring) But in 2019, a cruise ship plowed into a dock in the city.

♪ ♪ (people shouting) (hull scraping) NARRATOR: Luckily, there were only minor injuries.

But now the authorities only allow cruise ships in the Malamocco Canal, where they are free to travel at much higher speeds.

Luca believes this will increase the erosion.

♪ ♪ ZAGGIA: My opinion is, the lagoon, it's not suitable for large vessels.

We must be correct with the environment, because, uh, we inherited it from the past.

And we are in charge of it.

And this is what protects Venice from, from further damages.

♪ ♪ NARRATOR: Protecting the natural flood defense systems in the lagoon is key to the survival of Venice.

♪ ♪ And around the globe, the idea of using nature to counteract rising sea levels is gaining traction.

Ed Blakely directed the recovery effort in New Orleans after Hurricane Katrina.

♪ ♪ We've been removing salt marshes and these kinds of things that act as filters for the water that will come into a city.

♪ ♪ The floods that came in Katrina, the surge that was coming up the Gulf, the Mississippi, the lack of the trees meant it reached the city.

Had those trees still been there, New Orleans would have been saved.

♪ ♪ In my view, natural solutions are the best way to protect populations.

Basically putting nature back where it should be.

Mangroves are particularly effective in dealing with surges, because as the river rises, they absorb that, and they dampen the sea rise effect.

You can also start replanting.

Restoring the cypress trees and things that were in the canal systems that contain the water and hold it.

And building barrier islands that once were there.

Replacing them makes a lot of sense.

I think nature is our only ally in the future.

If we don't restore nature, we have little hope of restoring and keeping our cities.

♪ ♪ NARRATOR: But could Venice take the idea of working with nature one step further?

♪ ♪ Could the key to saving Venice be the geology beneath the city?

♪ ♪ It's an idea that engineer Pietro Teatini is exploring.

♪ ♪ TEATINI: The idea is, by injecting seawater into deep aquifers or deep reservoir below the lagoon bottom, to try to uplift the city of Venice around 25 centimeter.

This is something that can really be, be done, and in practice, it works.

♪ ♪ NARRATOR: Beneath Venice's lagoon, there are layers with different geological properties.

Some are impermeable clay.

These surround aquifers, strata of highly absorbent sandy deposits.

Injecting seawater directly into these aquifers would cause them to swell and push up on the layers above, lifting the whole of Venice.

It's an ambitious plan.

But lifting land by injecting water is a proven technology.

♪ ♪ In the 1930s, oil was pumped from the Wilmington Oil Field in California in such vast quantities that the land began to sink.

♪ ♪ By the late 1950s, it affected an area of 20 square miles.

And in some places, the ground had dropped 29 feet.

Engineers began injecting seawater under the ground, which lifted the land up and back to its previous level.

♪ ♪ Pietro and his team have calculated they could lift Venice for $100 million, a fraction of the cost of the MOSE.

TEATINI: The idea that we have is to put ten wells around Venice, centered on the Bridge of Rialto.

We inject different amount of water into each well.

And we adjust the pumping rate in order to have as uniform as possible uplifting of the city, but without generating any kind of cracks or fracture.

We reach this maximum uplift of about 20, 25 centimeter in ten years.

NARRATOR: Raising Venice nearly ten inches would decrease the impact of future surge tides and sea level rise in the city.

Working alongside the MOSE and the lagoon's salt marshes, it could reduce the risk of Venice flooding and help protect the city's centuries-old buildings.

♪ ♪ Venice was born out of its natural environment and clever engineering.

Adapting the lagoon's muddy islands offered Venetians a way to build their first homes.

Now, 1,600 years later, they have come full circle.

Faced with losing their city to climate change, once again, they are innovating with large-scale engineering and the restoration of their ancient lagoon.

Only by using multiple approaches can they hope to save Venice.

BLAKELY: My view of the future of Venice is that if it keeps going the way it's going, there will be no Venice in less than 50 years.

But if it changes its course, it can last another thousand years.

That's up to Venice.

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