Chicago Harbor Lock, Stop lock and dam at the mouth of the Chicago River, Chicago, US

Chicago Harbor Lock is a stop lock and dam at the mouth of the Chicago River within Chicago Harbor. Its chamber, 600 feet long, 80 feet wide and 22 feet deep, holds up to 100 vessels and is closed by two pairs of 30-foot sector gates. A concrete control tower with a glass-enclosed observation room rises beside the chamber, and a low pier with a small white building stands to the left.

The Sanitary District of Chicago constructed this lock between 1936 and 1938 to control water diversion from Lake Michigan and reverse the Chicago River's flow. The project was part of a broader effort to improve the city's water quality.

The lock is one of two entrances from the Great Lakes into the Chicago Area Waterway System; the other is the T.J. O'Brien Lock and Dam on the Calumet River. Its eight sluice gates, each 10 by 10 feet, sit along the piers of the controlling works.

The lock chamber is 600 feet long, 80 feet wide and 22 feet deep, with two pairs of 30-foot sector gates; a typical cycle takes 12 to 15 minutes for a two-to-five-foot level difference. Boaters pass through the chamber, while land visitors watch from the shore near the control tower and the small white building on the pier.

The lock chamber can hold up to 100 vessels at once, and its two pairs of sector gates stand 30 feet tall. Water level is changed by gravity, simply by partly opening and closing the gates.