Which of the following describes a safe water mark?

A safe water mark is a specific type of navigational buoyage used within the IALA Maritime Buoyage System. Its primary purpose is to indicate that there is safe water all around the buoy, which means it can be used as a reference point for vessels to navigate safely in the area.

When labeled as a navigational aid for all vessel types, it highlights its versatility and essential function. Safe water marks are particularly important for various crafts—including larger vessels that require more space for safe passage—as they provide critical information about the water depth and surrounding conditions.

In contrast, safe water marks are not limited to indicating deep water only, nor do they specifically mark underwater obstructions or signal groundings. Their role is broader, providing general guidance to all vessels, making choice C the most accurate description of a safe water mark.