- [Narrator] The Chicago River is one of the city's treasures.

(subway rumbling) This urban waterway is teeming with new life, a place to connect with the natural world in the midst of a modern metropolis.

Today's river would be almost unrecognizable to those who lived here during the 19th century when the river was treated like a sewer.

(gentle music) - The Chicago River, I think, one way we can put it is probably the city's toilet, the city's bathroom.

- We used the river as our sewer.

And whether that was human waste, industrial waste, commercial waste, anything.

- It all went into the river, and the river became very polluted.

- The water itself was not blue, not green.

It was various shades of brown.

- And the smell, we can only imagine the smell of this large sewer right through the heart of Chicago.

- [Narrator] Water from the Chicago River's north branch and south branch poured into the river's main stem flowing east through the center of the town, and emptying into Lake Michigan, the source of Chicago's drinking water.

- The river is flowing into Lake Michigan.

Where are we getting our drinking water then and now?

Lake Michigan.

- It was really water not fit for human consumption.

- [Narrator] Chicago became a town in 1833.

And from day one, it had troubles with sewage disposal and dirty water.

- We're talking about a frontier town, really a haphazard mix of houses, and stores, and stables.

Later on, dirt roads, wooden sidewalks.

It was largely a mess, livestock walking down the street.

- Not only was there no sewage treatment, there were no sewers so people would go to the bathroom in outhouses and privies.

They'd use chamber pots and perhaps, just toss it into the gutter.

And all of that would wind up in the river in one way or another.

- Public water supply didn't start until the 1840s so, prior to that, people had to use wells.

Well, that just cycled the wastewater on their own property.

- [Narrator] Chicagoans were unwittingly polluting their own well water.

Scientists hadn't yet discovered that disease was spread by microscopic organisms like bacteria found in dirty water.

- Clearly, we knew sanitation was important.

And where you didn't have good sanitation, you would see disease.

The prevailing theory of disease before germ theory was this idea of miasma, bad air, you're smelling bad air, as opposed to swallowing contaminated water.

- [Narrator] Year after year, Chicago was hit with epidemics of waterborne diseases.

One of the worst was cholera.

- Cholera is a really nasty disease.

What happens is very, very, very quickly, this bacteria starts to move through your body, and causes you to have just lots and lots of diarrhea.

And your circulatory system collapses and it's very contagious and so, you would see it move through a household, move through a neighborhood.

- [Narrator] Almost 700 Chicagoans died from cholera in the summer of 1849, that's 1 out of every 36 people.

- What was really scary about it is you could have a healthy Chicagoan and that person could get cholera and literally be dead within 24 hours.

- [Narrator] Chicago began to supply water from Lake Michigan to homes and businesses, but it only made things worse.

The untreated water was full of invisible, but deadly bacteria.

Another cholera outbreak in 1854 killed 1400 people.

Chicagoans were terrified.

Something had to be done.