Question 391Navigation General

The correct answer is D) the upstream end of the river wall. The display of 3 green lights in a vertical line indicates the upstream end of the river wall, which marks the entrance to the lock chamber. This is the signal that the lock is open and ready to receive your tow. The other answer choices are incorrect. Option A is wrong because 3 green lights indicate the lock is open, not that you should hold up. Option B is incorrect because the 3 green lights do not specifically indicate the lock chamber is open, just the entrance. Option C is wrong because the 3 green lights mark the river wall, not the land wall.