What does a number 4 buoy mean?

A number 4 buoy typically indicates a lateral marker in maritime navigation, specifically part of the IALA (International Association of Lighthouse Authorities) buoyage system. In the U.S. and other countries using the IALA A system, a number 4 buoy is usually colored green and may have a conical shape, signaling that it marks the left side of a channel when entering from the sea. It can also be used to indicate safe passage or the presence of hazards nearby. Always refer to local navigation charts for specific meanings and regulations.