Question 147Navigation General

The correct answer is D) 400 feet. The reason for this is that according to the U.S. Coast Guard regulations, descending boats waiting to enter a lock must be positioned at least 400 feet above the lock. This allows sufficient space for other vessels to safely approach and enter the lock without being obstructed by the waiting boats. The other answer choices are incorrect because they do not meet the 400-foot minimum distance requirement specified in the regulations. Boats positioned closer than 400 feet could potentially block traffic and create unsafe conditions near the lock.