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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Identify a buoy by combining its color and pattern with its shape, topmark, light, and location on the chart—not by color alone. First establish the buoyage region and the conventional direction of travel: lateral-mark colors reverse between IALA Regions A and B. Other common marks indicate a compass side with deepest water, a hazard, safe water, a special area, or a newly marked wreck.
Start with the buoyage system and chart
A buoy is a floating, moored artificial navigation mark. The International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) system describes six mark types: lateral, cardinal, isolated danger, safe water, special, and emergency wreck marking. Lateral colors depend on the region; the other five types are common to both regions. See IALA’s Maritime Buoyage System overview.
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Before interpreting a buoy, check the chart and local nautical publications for the waterway, its conventional direction of buoyage, and the mark’s intended meaning. That direction is generally from seaward, but the competent local authority establishes it. IALA’s general principles emphasize using aids to navigation alongside official nautical documents and prudent seamanship.
How to identify the six buoy types
| Mark type | What it indicates | Key identifying features |
|---|---|---|
| Lateral | Side of a navigable channel | Red or green; interpretation depends on IALA region and conventional direction. |
| Cardinal | Compass side of the mark where the deepest water lies | Black-and-yellow horizontal bands, paired black cone topmarks, and white flashing light patterns. |
| Isolated danger | A localized danger with navigable water around it | Black with one or more red horizontal bands; two black spheres on top. |
| Safe water | Navigable water all around; may indicate a fairway, mid-channel, or landfall | Red-and-white vertical stripes; a single red sphere on top. |
| Special | A special area or feature identified on the chart or in another nautical publication | Yellow, often with a yellow X topmark; shape can vary. |
| Emergency wreck marking | A newly discovered wreck or other hazard needing conspicuous marking | Blue-and-yellow vertical stripes and a yellow cross topmark. |
Lateral marks: channel sides
Lateral marks show the sides of a navigable waterway in its conventional direction of buoyage. You need both that direction and the applicable region to read red and green correctly:
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- IALA Region B: red marks starboard (right) and green marks port (left) when proceeding in the conventional direction.
- IALA Region A: red marks port (left) and green marks starboard (right) in that direction.
Do not apply the rule in the opposite direction of travel without checking the chart. A red buoy does not have one universal meaning across regions or directions.
In U.S. Region B waters, red aids generally carry even numbers and green aids odd numbers, with numbers increasing from seaward in the conventional direction. U.S. Coast Guard guidance also gives exceptions, including on Western Rivers; it describes red unlighted buoys as nuns and green unlighted buoys as cans. These are U.S. examples, not universal rules. Consult the U.S. Coast Guard’s navigation rules and aids guidance and current local information.
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Cardinal marks: the compass side with deepest water
A cardinal mark tells you that the deepest water in the area lies to its named side: north, east, south, or west. Read the black-and-yellow horizontal bands and the arrangement of the two black cone topmarks together; the cone arrangement distinguishes the directions. Cardinal buoys are commonly pillar or spar shaped, but shape by itself is not distinctive. IALA’s cardinal-mark guidance also specifies these white light rhythms:
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- North: continuous quick or very quick flashes.
- East: three quick or very quick flashes.
- South: six quick or very quick flashes followed by a long flash.
- West: nine quick or very quick flashes.
The east, south, and west counts follow a 3-6-9 pattern around a clock face; the long flash in the south sequence helps distinguish it. A cardinal mark identifies the safe side relative to that mark, but does not replace chart guidance for a route.
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Isolated danger marks: a hazard with water around it
An isolated-danger mark stands on or near a danger with navigable water around it. Look for a black buoy with one or more red horizontal bands and two black spherical topmarks. If lighted, it has a white group-flashing character, commonly in groups of two. Its appearance does not establish the full extent of the danger or a safe passing distance; use the chart and nautical publications.
Safe-water marks: navigable water all around
A safe-water mark indicates that navigable water surrounds it; it is not a danger mark. It can identify a fairway, mid-channel, or landfall. The identifying pattern is red-and-white vertical stripes, with a single red sphere as the topmark. The buoy can be spherical, pillar, or spar shaped. If lighted, it uses a white rhythm such as isophase, occulting, one long flash, or Morse code “A.” Check the chart to determine how the mark relates to your route.
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Special marks: a chart-defined area or feature
A special mark identifies an area or feature whose significance is given on the chart or in another nautical publication. It is yellow, may have varied shapes, and can carry a yellow X topmark; a fitted light is yellow. Yellow alone does not tell you what the area or feature means, so look it up in the relevant local information.
Emergency wreck marking buoys
IALA’s emergency wreck marking recommendation describes vertical blue-and-yellow stripes, a yellow cross topmark, and an alternating blue-and-yellow light. The marks are intended for newly discovered wrecks and other hazards that need conspicuous marking. If you encounter a possible wreck or hazard, follow current chart and authority information rather than relying on a general visual guide.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A practical way to identify a buoy
- Find the waterway on the current chart. Confirm local notices and publications, and identify the competent authority’s conventional direction of buoyage.
- Establish the region before reading lateral colors. Determine whether Region A or Region B applies and whether you are proceeding in the conventional direction.
- Compare several visible features. Note the color and banding, buoy shape, topmark, and any light color or rhythm. Treat numbers as a supporting clue only where local rules establish their meaning.
- Match the features to a mark type. Ask whether the mark indicates a channel side, a compass side with deepest water, an isolated hazard, safe water, a special area, or an emergency wreck.
- Use official chart information for decisions. Do not infer a hazard’s full extent, a safe passing distance, or a special area’s meaning from appearance alone.
What buoy appearance cannot tell you
- The correct red-or-green rule without context: Region and direction matter for lateral marks.
- A complete route or safe passing distance: A buoy’s visual type does not supply all the information needed to plan passage around a hazard.
- The local meaning of every special mark: Its significance may be defined only in a chart or nautical publication.
- Whether a buoy is still in its charted position: Buoy locations, local directions, chart corrections, and notices can change.
For a particular route or buoy, use a chart covering the actual boating area and check its edition and corrections alongside current local notices. IALA advises mariners to consult charts for further guidance on interpreting marks.
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