Editing Lateral mark (section)

=== Both regions ===

[[File:IALA Maritime Buoyage System Regions.svg|thumb|400px|{{legend|#d00| Region A is where port is indicated by red lights.}}
{{legend|#090| Region B is where port is indicated by green lights.}}]]

* port marks are square or have a flat top
* starboard marks are conical (or present a triangular shape) or have a pointed top.

The shape is an important feature, as colours cannot be distinguished in some light conditions, or by persons with red-green [[colour blindness]]. Marks may also carry unique markings of letters and numbers; these may be used to identify the mark as one indicated on a [[nautical chart]]. Likewise, a mark's light may flash in a distinctive sequence for the same purpose.

When a channel divides, as for instance a channel to a smaller harbour off a main river, then a ''preferred channel'' or ''bifurcation'' mark is used.  The mark has the same shape and main colour as a port- or starboard- hand mark for the main channel.  It bears in addition a horizontal band with the appropriate colour for the smaller channel.  For example: region A, main channel straight on, creek leading to marina to port.  The buoy where the channels divide would be a red cylindrical can or pillar with a cylindrical top mark.  Around the middle would be a green band.  In IALA region B the shape would be identical, but the main colour would be green with a red band.<ref>{{ Citation | title = Maritime buoyage system and other aids to navigation | publisher = IALA (International association of maritime aids to navigation and lighthouse authorities) | year = 2010|pages=10–11}}</ref>  See the buoy by the island in the diagram above.

In Region A only, the phrase "Is there any red port left?" (referring to the red colour of the fortified wine "port") may be used as a mnemonic, indicating that a red mark must be kept on the left when "returning" to (i.e., entering) a harbour or river.

In Region B only, the phrase "red right returning" may be used as a mnemonic, indicating that a red mark must be kept on the right when ''returning'' to (''i.e.'', entering) a harbour or river.