Aids to Navigation

Aids to navigation are like road signs for the water, and there are two systems that mark the waterways in the United States. The Federal U.S. Aids to Navigation (USATONS) system and the State Waterway Marking System (USWMS) are resources that assist boaters in determining position and course while warning of dangers and obstructions and marking routes. USATONS is a system that prescribes regulatory markers and aids to navigation that mark navigable waters in the U.S. USWMS is a system that prescribes regulatory markers and aids to navigation for navigable state waters. Each of the systems is a collection of devices that are external to the watercraft and include visual, aural and radar aids. Charts and other publications that map the location of these aids are available.

Unfortunately, citations are regularly issued for failure to obey regulatory markers. A proficient boater knows how to recognize and respond to all USATONS and USWMS aids and systems so that they can navigate safely and be aware of any special dangers or situations. After having completed this section, operators should be able to recognize and explain the functions of various buoys and should understand what to do in response to the specific circumstances identified by the navigational aids.

Because storms and wave action can move buoys out of place, boaters should not rely on Aids of Navigation alone for determining their boat’s position in the water

Federal U.S. Aids to Navigation (USATONS) System

U.S. waters are marked by the U.S. Aids to Navigation (USATONS) system to assist boaters in safe navigation. This system is built from a simple arrangement of various colors, shapes, numbers and light characteristics. Each aid to navigation has a specific purpose. They can help to determine location, aid in navigating away from hazards, and getting from one location to another. The USATONS system has been designed with a focus on promoting safe navigation in waterways.

Boaters must understand that the USATONS system is intended for use with appropriate nautical charts. Charts are essential for planning trips and navigating safely. 

Nautical chart

Beacons and buoys are the primary components of the USATONS system. Beacons are permanently fixed in place and range from lighthouses to small, single-pile structures. They can be located on land or in the water. Buoys are floating aids that come in all shapes and sizes. They are moored to the seabed and intended to convey information to boaters by their shape, color or symbols.

Lateral Aids to Navigation

Diagram of different Lateral Aids to Navigation

The USATONS Lateral Buoy System is the most common and uses red and green buoys to aid in general navigation by indicating the location of safe routes. Lateral buoys specify the side on which boaters may safely pass them.

Upstream Direction (“3R” Red Right Returning Rule)

Upstream direction beacons

The mnemonic phrase “red, right, returning” is a common and effective means by which boaters can remember how to use the lateral buoys to navigate appropriately. This simple phrase serves as a reminder of which side of the vessel the buoys should be on when the boat is travelling upstream or downstream. The phrase means that a boater should keep the red buoys on the right-hand (starboard) side of the boat when returning upstream. Also, each aid is numbered, and the numbers will increase as entering from seaward.

To be clear, the phrase “upstream” refers to any direction that is moving up-river, toward a shoreline, or into a harbor. It is also often used to refer to travel from an open body of water to a more constrained area.

Port Side (Odd-Numbered) Aids

Port side aids are also referred to as “left-hand” aids because they are to be kept on the left side of the vessel when it’s travelling upstream. Of course, port side aids should be kept on the right side of the vessel when it is travelling downstream. Port side aids are green in color.

Different types of port side aids

Port side aids are identified by odd-digit numbers, and come in four different variations:

·         Light

·         Lighted Buoys

·         Can

·         Day Beacon

Port side aids, if lit, will shine a green light that is flashed in one of the following patterns:

Port side buoys may have white odd numbers, while beacons may display green odd numbers.

Starboard hand 

Starboard side aids are also referred to as “right hand” aids and are red in color. These aids mark the right side of a channel and should be kept to the right (starboard) of the vessel when it is travelling upstream. As mentioned before, the mnemonic phrase “red, right, returning” is a common and effective means by which boaters can remember this concept.

Different types of starboard side aids

Starboard side aids are identified by even-digit numbers, and come in four different variations:

·         Light

·         Lighted Buoys

·         Can

·         Day Beacon

Starboard side aids, if lit, will shine a red light that is flashed in one of the following patterns:

Starboard side buoys may have white even numbers, while beacons may display red even numbers.

Preferred Channel Marks

Preferred Channel Marks are usually found at junctions of navigable channels, often marking wrecks or obstructions. Though they can be passed on either side, Preferred Channel Marks indicate which of the channels is safest by the color of the band at the top. If the band at the top is red, it is treated as a red aid (remember the 3R rule) and should be kept to the starboard side of the boat as it passes while travelling upstream. Boaters need to be aware that it may not always be possible to pass on both sides of the Preferred Channel Aids.

Different types of preferred channel marks

Non-Lateral Aids to Navigation


Dayboards are diamond-shaped and are used to assist the boat operator in determining his/her location on the water. They function like “You Are Here” markings on building maps. Appropriate and current nautical charts must be used in conjunction with the dayboards to determine location.

Safe Water Aids

Mid-channels, offshore points and fairways are marked by Safe Water Aids, which have unobstructed water on all sides. These aids can also be used by boaters travelling in offshore waters to determine the proximity of intended landfall. Safe Water Aids are usually lighted/unlighted buoys and may display a red topmark.

Safe Water Aids

Isolated Danger Markers

Isolated Danger Markers are true to their name in that they indicate an isolated danger that may be passed on all sides. They are placed on or moored on or near dangers, so they should not be approached closely without extreme caution.

Isolated Danger Marker

Range Dayboards

Range dayboards work in pairs as aids to navigation. When the dayboards and/or lights are lined up with each other (see figure below), they assist boaters in maintaining a safe course within a navigable channel. To determine whether a range may be safely travelled, an appropriate nautical chart must be consulted. Ranges are usually lighted (although not always) and display rectangular dayboards of varying colors. Ranges are lit 24 hours per day and may not display dayboards.

Regulatory/Informational Markers

Regulatory/ Informational Markers are used for various navigational aid purposes, including marking danger areas, controlled areas, boat-exclusion areas and displaying vital information. Their purpose is to alert boaters to various warnings and regulatory matters and they are identified by orange bands on the top and bottom of each white buoy. Regulatory and informational markers display black text and orange symbols, and, when lighted, may display any light rhythm except quick flashing and flashing (2). They can be buoys or beacons.

Examples of regulatory/informational markers include the following:

Different examples of regulatory/informational markers

Danger Marker

The orange diamond shape on a Danger Marker warns boat operators of hazards.

Restricted Operations Marker

The orange circle shape on Restricted Operations Markers indicates an area with regulated operations, such as speed limits or no wake zones.

Boat Exclusion Area Marker

The diamond shape with a cross indicates that boaters are excluded from the area. Usually, Boat Exclusion Area markers are found in swim zones and other prohibited areas.

Informational Marker

Markers with an orange square provide helpful information such as distances, directions and locations.

Intracoastal Waterway Marks

Intracoastal Waterway Marks

The Intracoastal Waterway (ICW) runs parallel to the Atlantic Ocean and gulf coasts from Manasquan Inlet, New Jersey to the Mexican border. This waterway is marked by its own special Aids to Navigation system that is identified by its unique yellow symbols. Aids with a yellow horizontal band simply mark the ICW while providing no lateral information. Lateral aids to navigation in the ICW system include:

  • Starboard side aids displaying yellow triangles– These should be kept to the right of the vessel when passing.
  • Port side aids displaying yellow squares– These should be kept to the left of the vessel when passing.

When following the ICW from New Jersey through Texas, the color navigation the aids appear on does not determine passing side. Just remember that yellow triangles should be kept on the right and yellow squares on the left.

Mooring Buoy

Mooring Buoy

The distinctive color scheme of Mooring Buoys is used to make them easily distinguishable from aids of navigation. Mooring Buoys are white with a blue horizontal band and may show a white light.

Special Marks

Special features or areas, such as anchoring, fish net areas, cables and pipelines, military exercise areas, jetties, etc., are marked by Special Marks. Special Marks are not intended to assist boaters in navigation.

Inland (State) Waters Obstruction Mark

Inland (State) Waters Obstruction Mark

Inland, or State, Waters Obstruction Marks are buoys that are used to warn boaters that an obstruction to navigation extends from the nearest shore to the buoy. They are black and white vertically striped. They communicate to boaters “do not pass between the buoy and the shore."