Locks No. 27
and Chain of Rocks Dam

Granite City, Illinois

Chain of Rocks Lock, also known as Locks No. 27, is situated on the southern end of Chouteau Island near Granite City, Illinois across the river from St. Louis at Mississippi River Mile 185.5. After 1940, only a single obstacle prevented the maintenance of a safe and reliable 9-foot navigation channel on the Mississippi River from St. Paul to New Orleans. This obstacle was a 17-mile series of rock ledges that began just north of St. Louis known as the Chain of Rocks Reach. This stretch of river in low water seasons was treacherous for towboats and barges, often requiring them to wait up to several days for the river to rise.

In the late 1940s and early 1950s the US Army Corps of Engineers designed and built a canal to bypass this area. A low water dam was built just below the north end of the canal and a lock was installed at the south end of the canal. These structures ensured that the entrance to the canal had a sufficient water depth for the towboats and barges.

The Chain of Rocks Dam (also known as Dam No. 27) is a non-moveable, low water dam and has no above water structure. The dam was built by dumping tons of rock into the river to create a small pool elevation upstream from the Chain of Rocks. Two small buildings that look like miniature castles sit in the middle of the river and house the water intakes for the St. Louis area water purification plant. The dam created a 13,000 acres pool that stretches nearly 28 miles.

Locks No. 27 consist of a 1200-foot main lock and 600-foot auxiliary lock and were opened in February 1953. Locks No. 27 are the southernmost locks on the Mississippi River and they are the only locks south of the confluence of the Mississippi River and Missouri River. Locks No. 27 moves more cargo than any other navigation structure on the Mississippi River.

Due to current security considerations public viewing of Locks No. 27 is very limited and visitors interested in how locks and dams work and the Mississippi River in general are encouraged to visit the Melvin Price Locks and Dam located north of Locks No. 27 in East Alton.  

Regional Locks and Dams - Get more information on the Locks and Dams in the Middle Mississippi River Valley from Lock and Dam No.19 in Keokuk, Iowa to and Lock and Dam No. 27 in Granite City, Illinois just north of St. Louis.
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