What is indicated by a lighted buoy with a red spherical top mark?

A lighted buoy with a red spherical top mark indicates a safe water buoy. Safe water buoys are used to mark navigable channels and are typically found in deep water areas. They inform mariners that they are in a safe area, free of obstacles or hazards. The spherical top mark, along with the red color, helps define the buoy's role and presence in the navigation system.

Safe water buoys are often utilized to guide vessels safely through channels and can be a point of reference in navigation. This mark allows a vessel to be assured that they can safely navigate past it without the immediate risk of grounding or collision with underwater hazards.

In contrast, other options like danger areas, restricted areas, or navigational hazards would be indicated by different types of buoys with various shapes, colors, and marking configurations to alert mariners to exercise caution or to keep a certain distance.