Aids to navigation, meaning the buoys, daybeacons, and lights the U.S. Coast Guard maintains on navigable waters, work like traffic signals for boats: color, shape, number, and light rhythm each carry a specific meaning under 33 CFR Part 62, and federal law makes it a crime to damage, move, or tie up to any of them. Learn the pattern once and you can enter an unfamiliar harbor anywhere in the country and know which side of the channel you belong on.
Red Right Returning
All U.S. navigable waters follow the IALA Region B buoyage system, which uses color and shape to mark the edges of a channel.1eCFR. 33 CFR 62.21 – General The rule every boater learns first is red right returning. When you are heading in from the sea or upstream on a river, keep red markers on your starboard (right) side and green markers on your port (left) side. Heading the other way, back out toward open water, the relationship flips.
Red markers are called nuns for their conical tops and carry even numbers. Green markers are called cans for their flat-topped cylindrical shape and carry odd numbers. Numbers increase as you move upstream, so passing green can “3” tells you green can “5” is farther inland.2eCFR. 33 CFR 62.25 – Lateral Marks That gives you a rough sense of your progress along the channel without checking a chart every few minutes. Stray outside the line of buoys and you are in uncharted depth, which is where hulls and propellers meet rocks.
Daybeacons and Dayboards
Not every navigation aid floats. Daybeacons are fixed structures permanently attached to the bottom or to land, from a single-pile post to a full lighthouse tower. Unlighted, they are daybeacons; fitted with a light, they are simply beacons or lights.3U.S. Coast Guard. U.S. Aids To Navigation System Each carries a colored board called a daymark that follows the same lateral logic as the buoys.
Red daymarks are triangular, echoing the pointed shape of a nun. Green daymarks are square, echoing the flat top of a can. From a distance the shape tells you which side of the channel you are looking at before you can pick out the color. Daybeacons don’t drift off station the way a buoy can after a storm, which makes them reliable references, but they are also fixed objects if you cut a corner too close.
Preferred Channel Markers
Where a channel splits into two navigable routes, a preferred channel marker tells you which fork is the primary path. These buoys have horizontal bands of both red and green. The top band is the key. If the top band is red, treat the buoy like a red nun and keep it to starboard when heading upstream, which puts you in the preferred channel. If the top band is green, treat it like a green can and keep it to port.2eCFR. 33 CFR 62.25 – Lateral Marks
At night, preferred channel markers display a composite group flash of two quick flashes followed by one flash. The light color matches the top band, either red or green.4eCFR. 33 CFR 62.45 – Light Characteristics That two-plus-one rhythm is unique to preferred channel marks, so if you see it, you know you are approaching a junction even before you can read the color bands.
Regulatory Markers
White buoys or posts with orange horizontal bands are regulatory markers. They don’t mark the edge of a channel. They communicate rules and warnings for a specific area, using an orange geometric symbol between the bands:
- Diamond: warns of a hazard such as a submerged rock, shoal, or wreck. Give the area a wide berth.
- Diamond with a cross: exclusion zone where boats are prohibited entirely, such as near a dam or a swimming beach.
- Circle: controlled area, often posted with a specific rule like no wake or a speed limit. These protect shorelines, docks, and swimmers.
- Rectangle: general information such as directions to a marina, fuel dock, or boat ramp.
Regulatory markers show up most on inland lakes and rivers, where recreational boaters share water with swimmers and shoreline property. Ignoring a no-wake circle can bring a fine that varies by jurisdiction, and the real cost is often the property damage a wake inflicts on moored boats and docks.
Safe Water, Isolated Danger, and Special Marks
Three more marker types round out the system for situations the lateral marks don’t cover.
Safe Water Marks
Red and white vertical stripes identify safe water marks, sometimes called fairway or midchannel buoys. You can pass them on either side, because they indicate navigable water all around rather than an edge. They typically mark the approach to a channel from open water or the center of a wide fairway. If lighted, they show a white light only.
Isolated Danger Marks
Black buoys with one or more broad red horizontal bands mark a specific hazard with navigable water all around it, like a single rock or wreck. They carry a topmark of two black spheres stacked vertically.5eCFR. 33 CFR 62.29 – Isolated Danger Marks The regulation warns that these marks are erected on or near the danger itself, so they should not be approached closely without special caution. Pass on either side, but give them room.
Special Marks
Solid yellow markers have no lateral significance and do not tell you which side of a channel you are on. They flag areas described in charts and nautical publications: anchorages, cable or pipeline corridors, traffic separation schemes, military exercise zones, and ocean data collection equipment. If lighted, they display a yellow light with a fixed or slow flashing rhythm.6eCFR. 33 CFR Part 62 Subpart B – The U.S. Aids to Navigation System
Reading Lights and Sounds at Night or in Fog
After dark or in fog, shape and color disappear. The system then relies on light rhythm and audible signals. Each buoy’s light follows a timing pattern a mariner can match to the chart:
- Flashing: the light is off longer than it is on. This is the most common rhythm for standard lateral marks.
- Occulting: the light stays on longer than it is off, with brief periods of darkness.
- Isophase: equal durations of light and dark.
- Composite group flashing: groups of flashes in a distinct pattern, like the two-plus-one used on preferred channel marks.
Many buoys also carry bells, gongs, or whistles activated by wave motion. The sounds are not as precise as a GPS fix, but they can keep you from running into the very object trying to protect you. If the light fails, the bell still works, and the other way around.
Western Rivers Work Differently
The standard lateral system applies on coastal waters and most inland waterways, but the Mississippi and other western rivers follow modified rules that can catch coastal boaters off guard.7U.S. Coast Guard. National ATON-CU Study Guide – Section 14 Inland
Aids on western rivers are not numbered, because the channel shifts so frequently that renumbering after every relocation would be impractical. In place of safe water marks and isolated danger marks, the system uses two specialized dayboards: diamond-shaped crossing dayboards where the channel moves from one bank to the other, and rectangular or triangular passing dayboards on straightaway sections. Mile boards on fixed structures display the distance in statute miles from a reference point, usually the river’s mouth, though the Ohio River counts from the headwaters.
Green aids mark the right descending bank and red aids mark the left descending bank. The word descending is the point. On a river, downstream replaces “returning from sea” as the reference direction. Heading downstream on the Mississippi, green markers should be on your right.
Federal Penalties for Interfering With a Marker
Several overlapping federal laws protect aids to navigation, and the penalties are steeper than most boaters realize.
Under 33 CFR Part 70, no person may take possession of, build upon, deface, destroy, move, or fasten a vessel to any aid to navigation maintained by the United States. Violations are a misdemeanor punishable by a fine of up to $25,000 per day, imprisonment from 30 days to one year, or both. Half the fine goes to the person who provided information leading to the conviction.8eCFR. 33 CFR Part 70 – Interference With or Damage to Aids to Navigation Any vessel used in the violation is also liable for the fine amount plus actual damages.
A separate statute, 14 U.S.C. § 543, makes it unlawful to remove, relocate, damage, make fast to, or interfere with any Coast Guard aid to navigation. It carries a fine of up to $1,500 per offense, and each day of continuing violation counts as a separate offense.9Office of the Law Revision Counsel. 14 USC 543 – Interference With Aids to Navigation; Penalty A third statute, 33 U.S.C. § 555, targets anyone who willfully injures, defaces, or destroys a Coast Guard aid, with penalties of a fine under Title 18, imprisonment up to one year, or both.10GovInfo. 33 USC 555
In practical terms, tying your boat to a buoy while you fish is a federal misdemeanor. So is anchoring in a way that blocks a range light. If your interference causes another vessel to run aground or collide, civil liability for the resulting damage falls on you on top of any criminal penalties. Recreational boaters face the same statutes as commercial operators.
Reporting a Damaged or Missing Aid
When you find a buoy that is missing, capsized, off station, or showing the wrong light, report it. The regulation directs mariners to contact the nearest Coast Guard facility by radio, phone, email, or through the Navigation Center’s web portal at navcen.uscg.gov.11eCFR. 33 CFR 62.65 – Procedure for Reporting Defects and Discrepancies Before calling, check the Light List to confirm you have the correct name and geographic position for the aid, because similar names in nearby areas cause confusion.
By radio, prefix your message with “Coast Guard” and transmit to a government shore station for relay to the District Commander. VHF Channel 16 (156.800 MHz) is the international distress and safety frequency monitored by the Coast Guard and most vessels required to carry radios.12Navigation Center. U.S. VHF Channel Information Safety broadcasts are then made on Channel 22A. For bridge-to-bridge collision avoidance, Channel 13 is the designated frequency, and vessels 20 meters or longer must monitor it in U.S. waters. A missing or damaged buoy is a hazard to every vessel that passes through the area after you, and reporting it is part of the deal for using the water.