This lock is located between the waters of Lake Michigan and the Chicago River. It was part of the project to reverse the course of the River. This was built by the Metropolitan Water Reclamation District of Greater Chicago. It was built between 1936 and 1938. It was originally built to prevent contamination of Lake Michigan water by the polluted water of the Chicago River. Currently it separates Chicago River Storm water from the Lake. It also regulates the amount of Lake water entering the River. In 1984, the operation and maintenance of the lock was transferred to the Army Corps of Engineers.
The lock is 600 feet long and 80 feet wide. It is 22 feet deep. Filling and emptying the lock occurs through a partially opened gate. The lock maintains a 2 to 5 foot water height differential between the Lake and the River.
The control house was replaced in 2007. The lock gates were renovated in 2011. The lock is operated 24 hours a day.