Channels and hazards need floating markers. A buoy is a floating aid to navigation, anchored to the seabed, that indicates safe water, wrecks, isolated dangers, or the edges of channels by its shape, color, and light character.

Lateral buoys mark port and starboard sides of a channel; cardinal buoys indicate safe water relative to a hazard; special marks serve other purposes. Mariners identify them by day shape and by night by light rhythm and color. Many now carry AIS transmitters as well.

Buoys drag, sink, or go dark in storms. Notices to mariners report defects. Navigators treat buoyage as a guide, not an absolute guarantee, and cross-check with depth and charted position. In poorly surveyed waters, a missing buoy can be the first sign of trouble.

• Floating, anchored navigational marker
• Identified by shape, color, and light character
• Marks channels, dangers, and special areas
• Requires verification against chart and depth