- [Narrator] On January 2nd, 1900 Chicago officials realized it was now or never.

(suspenseful music) In the gray light of dawn, a small group of Sanitary District trustees dressed in suits and ties, rushed to an earthen dam near Kedzie Avenue to try to break it open.

This was the last barrier holding back the Chicago River's waters from pouring into the new canal.

- They just kind of snuck in there, fearing that an injunction could come at any minute and shut them down for years.

So it was very much a priority, on Chicago's part, to get this done as fast as possible.

- [Narrator] But the ground was frozen solid.

In desperation, officials began attacking the dam with shovels.

- And that was tough because the ground was frozen.

Even using dynamite in frozen clay wouldn't move the clay.

(dramatic music) (footsteps crunching) - There was a small panic when two men came running toward the gathering.

The trustees feared they were delivering an injunction.

(dramatic music continues) But it was just a couple of newspaper reporters who had been tipped off.

For two hours, the group tried to break through the icy ground, attracting a growing crowd of spectators.

- The contractor had to keep chipping away with his dredge, and he finally made a cut and the water flowed.

- They breached this small makeshift dam and started to let the water in.

(water flowing) - [Narrator] A great shout went up from the crowd as the dam broke open.

- I think it was a sense of relief, but it was kind of muted by this ominous threat, either from judges in Illinois or at the Supreme Court.

- [Narrator] Sanitary District officials posed for a celebratory photo and almost got swept away by the rushing water.

- And ever since the Chicago River flow has been reversed, to the benefit of the city.

- [Narrator] People in Chicago started noticing something different about the river.

- Like these stories of people just being amazed by seeing clear, transparent ice in the river.

It would've been like, "Oh my goodness, like we can do this, "like we can bring public health to this city."

- It was a miracle, you know, the river ran clear.

It was wonderful.

- The Chicago Sanitary and Ship Canal took eight years to complete and it cost $33.5 million.

Adjusted for inflation, that would be more than a billion dollars today.

- [Allison] It achieved its mission, which was to protect our lake and the water supply.

- As a result, the city becomes a much more hospitable place.

African Americans are attracted to Chicago's growth as an industrial hub.

They come here seeking jobs.

- And Chicago went from being one of the least healthy cities to one of the healthiest cities.

We cut death rates somewhere between a third to half for all of these waterborne diseases, which is pretty amazing.