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IALA Buoyage System

As with the road, there are a number of rules and signs to help keep us safe and informed about the area. Buoys are the primary method of information on the sea (and in many rivers) and have an internationally recognised set of colours and shapes depending on the meaning (also known the IALA system), so are easily understood wherever you are in the world. Here are a few examples of the most common ones:

Be aware that Britain, Europe, Asia, Australia and Africa are in IALA Region A, which is described in this article. However, the Americas, Philippines, Japan and Korea are all in IALA Region B, which has the layout and shape of channel markers reversed. 

Lateral markers

Channel Cross-Section
A channel is an area of deep water (sometimes natural, sometime dredged), which is used like a main road into a harbour. These are often busy; most craft are restricted to them, otherwise they would run aground. Those operating small craft may not be as restricted as larger craft, but should take care when crossing channels to avoid collision. A set of buoys indicate the channel, so if you are new to an area you are aware of its whereabouts and can navigate accordingly.

There are two types of channel markers (known as lateral markers): a red can-shaped buoy and a green cone-shaped buoy. Sometimes red and green posts are used instead of buoys, but they have the same meaning. If lit, the red markers have a red light and the green markers have a green light. These buoys are laid out on either side of the channel (like Cat’s Eyes on the motorway) with the green buoys all along one side and the red on the other. By staying between a red lateral marker and a green lateral marker you know you are in the deep water channel.

The red can-shaped buoy is the port lateral marker, whilst the green cone-shaped buoy is the starboard lateral marker. A simple phrase to help you remember (based on port the drink) is: “There is no red port left in the bottle”.

They are laid out leading into the harbour. This means that if you are travelling along the channel into the harbour then the red markers would be on the boat’s port (left) side and the green markers would be on the boat’s starboard (right) side. This is useful to know, as you may only be able to see one marker, however you are still able to work out if you are in the channel or not.

Remember to stay as far to the right (starboard) as possible when using a channel. 

Safe water markers

Safe water markers indicate safe water (hence the name). They can be used in a variety of different circumstances, for example in mid channel to mark a centre line or turning point (in which case they should be passed to port), the safest route under a bridge or to land. They have vertical red and white stripes with a single red sphere on top. It has one long white flash of light then pauses. 

Isolated danger markers

Isolated Danger MarkerIsolated danger markers indicate a small, specific hazard (usually a rock) with safe water in all directions around the marker. You can pass them on any side, but remember to not get too close. They are coloured black and red and have two black spheres on top. Its light flashes twice then pauses. 

Cardinal markers

Cardinal Markers
Cardinal markers are used to denote where there is a hazard and in which direction there is safe, deep water. Generally, hazards indicated by cardinal markers are wrecks, reefs and other shallow areas.

Cardinal markers have two cones on top pointing in specific configurations, depending on the direction of deep water in relation to the marker. The markers are also painted black and yellow, with the black paint located where the cones point.

While the north (both cones pointing up) and south (both cones pointing down) are easy to remember, the arrangement of the other two are a bit more difficult. A simple trick is to see that the east cardinal marker’s cones (top pointing up, bottom pointing down) are shaped like an EASTer egg.

The lights on cardinal markers also flash in a specific way, so you can tell which one they are even in low visibility conditions. To help you remember the number of flashes of light (before a long pause), think of a clock face. East flashes three times, south flashes six times (followed by one long flash to make it more distinctive), west flashes nine times, and north flashes continuously.

Remember that cardinal markers point in the positive. That is you stay on the side it directs, such as west of a west cardinal marker.


Sometimes Leads are used to guide boats into port or along safe stretches of water. They are usually large orange triangles, which when aligned correctly form an hourglass shape (that is the tips of the triangles meet) from your perspective. To use them you need to manoeuvre your boat until both Leads are aligned exactly. If you have achieved this then you know that you are in safe waters. As long as you are moving towards, or away, from them they should not misalign. 

Special markers

Special Marker
Special markers indicate a specific feature (noted on the admiralty chart for the area) and are not necessarily used for navigation. Examples of features for which special markers are used include pipelines, cables and recreation areas. They are coloured yellow and have a yellow X on top. If lit, they have a yellow flashing light.