What is the main purpose of a buoy with green flashing lights?

A buoy with green flashing lights is used primarily to mark navigable channels. The color green, along with its flashing light pattern, is a clear indication to mariners that they are approaching the right side of a channel when proceeding upstream. In many regions, these buoys are part of the system set to indicate preferred channels and guide vessels safely, ensuring they stay within the navigable area while avoiding hazards such as shallow waters or obstructions.

Other choices, while they describe important navigational concepts, do not accurately align with the specific function of a buoy marked with green lights. For instance, a buoy that indicates safe water would traditionally be white, while buoys marking hazards or tide information would use different color codes or signals. Therefore, the green flashing light specifically denotes guidance for navigating channels, making it a vital tool for maritime safety.