The Lock & Dam is named for Thomas J. O’Brien, who was a U.S. Representative for the 6th District of Illinois from 1933 to 1938 and again from 1943 to 1964.

[1][2] The lock contains a pair of sector gates at either end, which were chosen as they both reduce the cost of engineering and are more conducive to operations in a waterway which can reverse direction.

[4] The lock and dam are used to maintain a 9-foot navigation channel, and for flood control purposes, primarily to limit diversion from the lake during normal periods, and mitigation of backflows into Lake Michigan during large storm events which reverse the direction of the river.

Nearly as soon as its completion, there was already lobbying by various industries along the waterway to expand the size of the lock, which measured 360 by 50 feet (110 m × 15 m).

A report by the United States Army Corps of Engineers (USACE) in 1933 proposed, among other things, expanding the size of the lock to 600 by 110 feet (183 m × 34 m) to improve navigation.