That its famous river, the Seine, would be a key fixture of the Games, including an historic Olympics opening ceremony.

The first held outside of a stadium, for which French officials initially said there is no plan B.

And that open water swimming events would be held in it.

It's not hard to see why.

The Seine runs along some of Paris' most famous landmarks, like the Eiffel Tower and Notre Dame.

The thing is, swimming has been banned in the Seine for a century.

And that's because the river Seine has human s*** in it.

(Speaking in French) Yes, for me, it's total nonsense.

I think the Seine is sill polluted and I'm not sure that the swimmers will emerge unhared after this swimming session.

Like many urban waterways around the world, the Seine takes on sewage overflow during heavy rain when city's underground sewer systems get overwhelmed with stormwater.

Hidalgo even said she would take a swim in the Seine herself ahead of the Games.

French President Emmanuel Macron promised the same thing.

They say they're confident because of an enormous underground infrastructure project they've built near the river.

To ensure, as much as possible, that it won't s*** on their parade.

This isn't the first time Olympic open water swimming events — the triathlon, paratriathlon and marathon swimming — were at risk of being canceled last minute due to water quality issues.

We saw some of the same headlines during the 2020 Olympics in Tokyo and the 2016 Olympics in Rio de Janeiro.

In both cases, they pulled it off.

And Paris hopes to do the same.

But the journey to clean up the Seine hasn't come without a few setbacks.

A preliminary event in the river scheduled for August 2023 was canceled when water analysis showed an unacceptable amount of E. coli in the water.

E. coli are bacteria that originate in the intestinal tracts of warm-blooded animals.

Presence of them in water is a strong indicator of recent fecal contamination, which can make you very, very, very sick.

In order for an open water swim event to be given the go-ahead, water analysis reports must be submitted no more than 48 hours prior to competition.

Those samples cannot exceed more than 1,000 CFU colony-forming units of E. coli per 100 milliliters of water,

and 400 CFU of Enterococci, another bacteria associated with feces.

Test results published just four months ahead of the Games showed that river samples taken at this bridge, the site of open water swimming events, still failed to get under that crucial 1,000 number for permissible levels of E. coli.

You can see where this contamination is coming from by taking a look at this 1852 map, showing how the original Paris sewer system was built.

It dumps right into the Seine.

Which is gross, but it's not a problem that's unique to Paris.

Many urban sewer systems work this way.

Before I get into that, though, I want to tell you about the sponsor of today's video, BetterHelp.

I don't know about you, but this year feels like it has flown by, and I can't believe we're halfway through the summer already.

Therapy is a great way to ground yourself in the present and help you set achievable goals for your mental health for the next six months.

But finding time to talk to a therapist can be hard.

That's where BetterHelp comes in.

It's entirely online, designed to be flexible, convenient, and suited to your schedule.

Just fill out a brief questionnaire to get matched with a licensed therapist, and switch therapists anytime at no additional charge.

Talk therapy has definitely been helpful for me, and if it's something that you want to try out too, get started with BetterHelp.

Take a moment, visit betterhelp.com slash voxvideo to get 10% off your first month.

Many cities that built sewer systems in the mid-1800s to early 1900s, like Paris did, installed what's known as a combined sewer system.

In a combined sewer system, the same pipes that handle wastewater also handle stormwater, which gets collected through storm drains in the street.

Everything gets sent along to be processed at water treatment facilities, and then cycles out to the natural environment.

When it rains a lot, the sewers can get too full.

When this happens, rather than flooding back into the street, the excess combined wastewater and stormwater gets partially redirected to a nearby waterway.

Which is why E. coli levels in water can spike dramatically in the hours following heavy rain.

It's because that water was recently contaminated with s**t.

So you'll see signs near combined sewer outfalls that prohibit swimming after heavy rain.

If that happens during the Olympics, it could mean canceling open water swimming events.

So Paris built a giant tank.

This 13.2 million gallon capacity underground reservoir and tunnel is part of a $1.5 billion U.S. dollar infrastructure project that aims to clean up the Seine.

It's called the Austerlitz Basin, built near the Austerlitz metro station right by the Seine, with the tunnel running under the river to the sewers.

French officials opened the basin less than three months ahead of the Olympics opening ceremony, which is scheduled for July 26th.

I'll let this guy explain how it works.

(Speaking in French) The mixture of wastewater and rainwater during the more intense episode will arrive through this pipe and fill the basin to its full capacity.

And wehn the pool, the rain is over, the basin is emptied by a systen for pumping much smaller pipes that will empty into the sewer on Boulevard de l'Hôpital.

Basically, the system will hold excess water so the sewers don't get overwhelmed in a heavy rainstorm.

And then it will methodically release the water back through the sewer system.

Reservoirs like this have worked in other cities with big populations, like the Thornton Composite Reservoir outside of Chicago, which can hold nearly 8 billion gallons of wastewater.

And this combined sewer outflow facility in the Perdigat Basin in New York, designed to prevent contamination of the basin and nearby Jamaica Bay.

The Austerlitz Basin isn't designed to clean the Seine.

That's an ongoing, multi-pronged process.

This project was built to prevent further, and sudden, contamination of the Seine from combined sewer overflow.

The goal, according to French officials, is to resort to opening the sewer overflow gates that dump into the Seine no more than twice a year, compared to the current rate of 10 to 15 times per year.

Paris will continue testing as the Olympics rapidly approach, but Hidalgo and Macron have yet to swim in the Seine.

If it all goes perfectly according to plan, a significant rainstorm could still contaminate the Seine, forcing open-water swimming events to be postponed.

(Speaking in French) There are things we won't be able to control, it's impossible.

So, there are, for example, retention basins that have been built.

But if there's a huge storm where you end up with a long rainy period, well, that's something we can't predict.

The idea of making the Seine swimmable again goes beyond just the 2024 Olympic Games.

It seems to be a good thing to start last in this annual race through Paris, because the River Seine gets so full you could almost walk over the swimmers in front.

It brings the city back to a time when the river was a place for Parisians to cool off in the summer instead of a biohazard.

Once the Olympics are over, that becomes the next phase of this project.

According to Mayor Anne Hidalgo, three swimming sites in the Seine will open to the general public in 2025, thanks to the Games.

(Speaking in French) Almost 100 years after the ban on swimming in the Seine, yes, my friends, we will once more allow swimming in the Seine.

As for the plan to host the opening ceremony along the Seine, French President Emmanuel Macron has now said that there are backup plans if the security risk is too high.

Whether or not open-water swimming will be possible can only be determined hours before the events and will be at the mercy of rain.

Meaning, making the Seine swimmable in time for the Olympics is going to take a lot of work and a lot of luck.