Illustration D037NG below represents a movable dam. If there is high water and the wickets are down so that there is an unobstructed navigable pass through the dam, what light(s) will be shown at B if the lock walls and piers are not awash?

Correct Answer: Option C — Three red lights

Federal regulations for movable dams stipulate that three red lights displayed horizontally or vertically at position B indicate the absolute closure of that section, warning mariners that the pass is obstructed and impassable.