What does an inland waters obstruction marker signify?

An inland waters obstruction marker signifies an obstruction to navigation. This type of marker is used to indicate underwater hazards that could pose a danger to vessels, such as rocks, shoals, or other debris that might impede safe passage. By highlighting these hazards, the marker helps boaters avoid potential accidents or damage to their vessels, thereby promoting safer boating practices. Knowing the meaning of these markers is crucial for maintaining safety on the water, as it ensures that boaters remain vigilant and aware of their surroundings. The other choices refer to different types of markers or areas indicating specific activities or restrictions, which do not apply to obstructions.