The Marseilles Lock and Dam, also known as Lock and Dam 5, is a lock and dam complex on the Illinois River at Marseilles, Illinois. The complex includes a lock, dam, control station, boiler house, and a 2.5 miles (4.0 km) section of navigation canal. The state of Illinois began work on the complex in 1920 by digging the canal, which was completed in 1925. The state also began construction on the lock, dam, and control station; however, due to financial difficulties these projects were finished by the U.S. Army Corps of Engineers. Walter Mickle Smith was chief design engineer for the complex. The complex was completed in 1933.
On April 18, 2013, the uninspected towing vessel Dale A. Heller, pushing a tow of 14 barges, allided with the dam complex during a period of exceptionally high water flow. Seven barges impacted the dam itself, and four of these sank. Gates 2 and 3 were rendered inoperative and gates 4, 5, and 6 were damaged but remained operational. Damage to the gates contributed to flooding in the city of Marseilles. Repairs to the dam were estimated to cost forty to fifty million dollars.