Lateral mark

Each mark indicates the edge of the safe water channel in terms of port (left-hand) or starboard (right-hand).

A vessel heading in the direction of buoyage (e.g. into a harbour) and wishing to keep in the main channel should: Marks are distinguished by their shape and colour, being red or green.

Likewise, a mark's light may flash in a distinctive sequence for the same purpose.

For example: region A, main channel straight on, creek leading to marina to port.

In IALA region B the shape would be identical, but the main colour would be green with a red band.

Visual Buoyage - Region B - By day.
A Region A lateral mark, showing both the green color and the triangular symbol, denoting the channel at the entrance to the Port River near Adelaide , South Australia
System A: Red port / green starboard marks when entering from sea into Le Palais , France
Region A is where port is indicated by red lights.
Region B is where port is indicated by green lights.