Chain of Rocks Lock
Chain of Rocks Lock, also known as Locks #27, is a lock situated on the southern end of Chouteau Island near St. Louis, Missouri on the Upper Mississippi River. Its associated dam is just downstream of the Chain of Rocks Bridge and the lock is located over three miles (5 km) south east, on the Chain of Rocks canal bypassing an unnavigable portion of the river. The 1200 feet (366 m) main lock and 600 feet (183 m) auxiliary lock were built in the late 1940s and early 1950s to allow a by-pass of the Chain of Rocks lying in the main channel of the Mississippi River. This stretch of river in low water seasons was treacherous for commercial tow boats and barges, often requiring them to wait up to several days for the river to rise. Lock 27 is the only lock on the Mississippi River System without a man made dam. Tons of rock were laid in the Mississippi to create a small pool elevation upstream from the Chain of Rocks. The drop at Locks 27 can vary from a few feet to over a ten foot drop depending on the river stage. The Chain of Rocks Lock is operated by the St. Louis District of the U.S. Army Corps of Engineers. Locks #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. As such, the Locks move more cargo than any other navigation structure on the Mississippi River.