One of the emergency dams at the upper end of one of the sets of locks on the Panama Canal. The photographer is on the port side of a passenger cruise ship passing through the lock looking at the close detail of the structure. Emergency dams could be swung across the locks at the upper end of every flight. These consisted of swinging bridges, from which girders were lowered to the lock floor; steel shutters could then be run down these girders to block the flow of water. In the late 1930s, these original dams were replaced by new dams, which were raised out of slots in the bottom of the lock chambers.