The system consists of lateral, cardinal and other buoys, such as isolated danger and safe water marks. Buoys can be distinguished from each other by
- the colour of their light and flashing sequence
- the colour and combination of colours on the buoy
- the shape of the topmark
This marking scheme is designed to enable mariners to identify a buoy if the light is extinguished and /or the topmark is missing.
Lateral buoys mark well defined channels and indicate port and starboard hand sides of the route to be followed, for port hand marks the buoy and light are coloured red, for starboard marks these are green.
Cardinal buoys are used in conjunction with a compass to indicate where a mariner may find the best navigable waters. They are coloured yellow and black and have white flashing lights.