WTTW News Explains

WTTW News Explains: How Does the Chicago Harbor Lock Work?

Some pretty famous people have been given a symbolic key to the city of Chicago.

And then there’s this guy. The Chicago Harbor Lock lockmaster.

He controls access to the city’s real front gate, so to speak.

That gate is the Chicago Harbor Lock: a 600-foot-long, 80-foot-wide chamber that separates the Chicago River from Lake Michigan.

It’s the second busiest harbor lock in the nation, and it’s right there next to Navy Pier.

The Harbor Lock was built in the 1930s as part of the project that famously reversed the flow of the Chicago River.

The whole point of that engineering feat was to keep wastewater out of the lake. But what about other floaters? Namely the thousands of boats that travel back and forth between the river and lake every year.

The lock manages that traffic — and not just to avoid gridlock.

It’s needed because the river is anywhere from one to four feet lower than the lake.

So think of the lock as an elevator.

Boats in the river are basically at ground level, and the lock gives them the boost they need to get to the lake.

Here’s how it works.

Boats coming from the river line up in a holding area outside the lock, waiting for signals.

A red light means “Do not enter.”

Yellow gives government and commercial boats the OK to move into the lock.

And green means go for recreational boaters.

As many as 100 boats can fill the lock at one time.

Once everyone’s in position, the elevator operator, er, lockmaster shuts the gate behind them to cut off the river. Next, the gate to the lake cracks open.

Lake water slowly fills the lock, and boats ride up with the rising level.

Once the lock is even with the lake, the gates open wide and boats exit into the open water.

The steps are reversed for boats returning to the river from the lake. They ride the water-vator back down to river level.

The whole process takes about 10 to 15 minutes. And it’s repeated more than 10,000 times every boating season.

Another hard-working feat of engineering from The City That Works.

Note: The lockmaster depicted in the animation has since retired. 

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