A yellow buoy may mark which of the following?

A yellow buoy is commonly used to signify a spoil area. Spoil areas are locations where dredged material is deposited, and these buoys help inform boaters that they should avoid entering these zones to prevent potential hazards associated with underwater obstructions or changes in the water depth created by the material. This specific marking is crucial for maintaining safe navigation and protecting both vessels and the marine environment.

The other options represent different types of markers or regulations. Safe harbor areas are typically marked by green or red buoys, danger zones may be indicated with specific shapes or colors that depict immediate hazards, and no-wake zones often use other colors or represent specific regulations. Understanding these designations is essential for safe boating practices.