CHICAGO UNCOVERED: See how the Chicago Harbor Lock works

CHICAGO (WLS) -- 24/7, 365, the US Army Corps of Engineers operates the Chicago Harbor Lock to keep boat traffic flowing and help avoid flooding on the Chicago River.

Tyrone Valley, the Chicago Harbor Lock's Lockmaster, said flood control is the lock's primary purpose. If there's enough runoff in the Chicago River, Valley explained, his team will open the lock's river-side gates so water will move into the lock chamber; that water can then be released into Lake Michigan.

The other big job for the lock: bringing boats from Lake Michigan into the Chicago River and vice versa. Valley said the river is typically about 5 feet lower than the lake.

"It's a water elevator," Valley explained.

To bring you from one floor to another, Valley's team will "crack the gates open" so that water flows in, equalizing the level. For example, if a boat is on the river and wants to go onto the lake, the river-side gates will open, the boat will enter the chamber, and the river-side gates will close behind. Then, the lake-side gates will just barely slide outward so that water begins to flow into the chamber, causing the water level to rise. Once that level goes up five feet (Valley said this takes about 5-7 minutes on average), the lake-side gates fully open and the boat moves out. Reverse the process for a boat going onto the river.