sentences:  Its associated dam is just downstream of the Chain of Rocks Bridge, and the lock is located over southeast on the Chain of Rocks canal.The canal and locks allow river traffic to bypass a portion of the river that is unnavigable in low water due to an anticlinal exposure of bedrock in the river—a "chain of rocks".The canal, main lock, and 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.