Aids to Navigation

Table of Contents

Nav Aids on TheBoaters

In our effort to contribute to the boating community, TheBoaters has prepared a video guide to understand the US Aids to Navigation.

To see the nav aids in action, go to our explore section and heave fun!

Aids To Navigation System

The waters of the United States and its territories are marked to assist navigation by the U.S. Aids to Navigation System. This system employs a simple arrangement of colors, shapes, numbers and light characteristics to mark navigable channels, waterways and obstructions adjacent to these.

Aids to Navigation can provide a boater with the same type of information drivers get from street signs, stop signals, road barriers, detours and traffic lights. These aids may be anything from lighted structures, beacons, day markers, range lights, fog signals and landmarks to floating buoys. Each has a purpose and helps in determining location, getting from one place to another or staying out of danger. The goal of the U.S. Aids to Navigation System is to promote safe navigation on the waterway.

The U.S. Aids to Navigation System is intended for use with Nautical Charts. Charts are one of the most important tools used by boaters for planning trips and safely navigating waterways. Charts show the nature and shape of the coast, buoys and beacons, depths of water, land features, directional information, marine hazards and other pertinent information. This valuable information cannot be obtained from other sources, such as a road map or atlas.

The primary components of the U.S. Aids to Navigation System are beacons and buoys.

Beacons are aids to navigation structures that are permanently fixed to the earth's surface. They range from lighthouses to small, single-pile structures and may be located on land or in the water. Lighted beacons are called lights; unlighted beacons are called daybeacons. Beacons exhibit a daymark to make them readily visible and easily identifiable against background conditions. Generally, the daymark conveys to the boater, during daylight hours, the same significance as does the aid's light or reflector at night.

Buoys are floating aids that come in many shapes and sizes. They are moored to the seabed by concrete sinkers with chain or synthetic rope moorings of various lengths connected to the buoy body. They are intended to convey information to the boater by their shape or color, by the characteristics of a visible or audible signal, or a combination of two or more such features.

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Private Aids to Navigation

A Private Aid to Navigation is a buoy, light or daybeacon owned and maintained by any individual or organization other than the U.S. Coast Guard. These aids are designed to allow individuals or organizations to mark privately owned marine obstructions or other similar hazards to navigation. For further information, contact your local Coast Guard District Aids to Navigation Office.

The U.S. Army Corps of Engineers regulates the placement of mooring buoys in all navigable U.S. waters. Those wishing to establish mooring buoys need to contact their local Army Corps of Engineers.

Safety Tips

  • A safe boater will always have the appropriate nautical chart(s) onboard their vessel. The exact meaning of an aid to navigation may not be clear to the boater unless the appropriate chart is consulted.
  • Boaters who pass too close to a buoy risk collision with a buoy, the buoy's mooring, or with the obstruction which the aid marks. Boaters must not rely solely on any single aid to navigation for determining their position, particularly buoys. Environmental conditions, seabed slope, composition, and collisions or other accidents may cause buoys to shift from their charted positions, sink or capsize.
  • Boaters should not come close to beacons due to the danger of collision with riprap (stones/broken rocks), structure foundation, or with the obstruction/danger which the aid marks. Always maintain a safe distance from all aids to navigation.

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Lateral System (As Seen Entering From Seaward)

Port Side Odd
Numbered Aids

green square Green Light Only

Flashing (2)
Illustration of patterns of flashing green lights for port side odd numbered aids.
Flashing
Flashing indicates single short flashes separated by pauses
Occulting
Occulting indicates single long flashes separated by pauses
Quick Flashing
Quick flashing indicates a very rapid sequence of single flashes
ISO
ISO indicates medium length single flashes
  • Illustration of a green light, which is a green square with dark green border and a green numeral 1 in the center. The light is atop the square. Chart mark for the light, which appears as a black circle with a magenta teardrop shape above it to the upper right side. First caption read "1" and second caption reads FI G 6 s.
    Light
  • Illustration of a lighted buoy, which is a cylindrical green structure with a square in the upper left quadrant, a white numeral 9 in the upper right quadrant, and the light affixed atop. Chart mark for a lighted buoy, which appears as a magenta circle with a green diamond affixed to the upper right side. First caption reads G "9" and second caption read FI G 4s.
    Lighted Buoy
  • Illustration of a can, which is a narrow cylindrical structure with a square in the upper left quadrant and a white numeral 9 in the upper right quadrant. Chart mark for a can, which appears as a clear circle with a green diamond affixed to the upper right side. First caption reads G and second caption reads G "9".
    Can
  • Illustration of a daybeacon, which is a pale green square with a dark green border and a numeral 5 in the center, affixed to a pole. Chart mark for a daybeacon, which appears as a green square. First caption reads GR and second caption reads C "5".
    Daybeacon

Preferred Channel
No Numbers-May Be Lettered

Preferred
Channel To
Starboard
Topmost Band
Green

green square Green Light Only

Composite Group Flashing (2+1)
Illustration of composite group flashing green light, which indicates two short flashes, followed by a medium pause and one short flash; the sequences are separated by a long pause.
  • Illustration of a lighted buoy, which has a green platform, with a rectangular structure that is red on the bottom and green on top. A square appears on the upper side of the green portion, and a white letter B appears on the right side of the green portion. A green light is affixed to the top. Chart mark for lighted buoy, which appears as a magenta circle with a diamond that is magenta on the bottom and green on top affixed to the upper right side. First caption reads GR "A" and second caption reads FI (2+1) R 6s.
    Lighted
  • Illustration of a daybeacon, which is a square that is green on top and red on the bottom, with a corresponding border of dark green and dark red. The letter U appears in the center. It is affixed to a post. Chart mark for daybeacon, which appears as a white square. First caption reads GR and second caption reads "U".
    Daybeacon
  • Illustration of a can, which is a narrow cylinder that is green on the bottom, has a red band above the mid-point, and a green band above the red band. A square appears on the upper left side and a white letter S appears on the upper right side. Chart mark for can, which appears as a clear circle with a diamond that is green on the top and magenta on the bottom affixed to the upper right side. The first caption reads GR and the second caption reads C "S".
    Can

Preferred Channel
No Numbers-May Be Lettered

Preferred
Channel To
Port
Topmost Band
Red

red square Red Light Only

Composite Group Flashing (2+1)
Illustration of composite group flashing red light, which indicates two short flashes, followed by a medium pause and one short flash; the sequences are separated by a long pause.
  • Chart mark for lighted buoy, which appears as a magenta circle, with a diamond that is green on the bottom and magenta on top affixed to the upper right side. First caption reads RG "B" and second caption reads FI (2+1) R 6s. Illustration of a lighted buoy, which has a red platform, with a rectangular structure that is green on the bottom and red on top. A square appears on the upper side of the red portion, and a white letter B appears on the right side of the red portion. A red light is affixed to the top.
    Lighted
  • Illustration of a nun buoy, which appears as a narrow cylindrical structure with a tapering top. The structure is red, with a green band across the upper half. A red square appears in the upper left, and a white letter C appears on the right side of the green stripe. Chart mark for nun buoy, which appears as a clear circle with a diamond that is magenta on top and green on the bottom affixed to the upper right side. First caption is RG and second caption is N "C".
    Nun
  • Illustration of a daybeacon, which appears as a triangle mounted on a pole. The top half is red with a dark red border; the bottom half is green with a dark green border. A red letter G appears in the center. Chart mark for daybeacon, which appears as a white triangle. First caption is RG and second caption is "G"
    Daybeacon

Starboard Side
Even Numbered Aids

red square Red Light Only

Flashing (2)
Illustration of patterns of flashing red lights for starboard side even numbered aids.
Flashing
Flashing indicates single short flashes separated by pauses
Occulting
Occulting indicates single long flashes separated by pauses
Quick Flashing
Quick flashing indicates a very rapid sequence of single flashes
ISO
ISO indicates medium length single flashes
  • Illustration of a light, which appears as a red triangle with dark red border mounted on a pole. A red numeral 2 appears in the center and a red light is affixed to the top. Chart mark for light, which appears as a black circle with a magenta teardrop shape above the upper right. The first caption reads "2" and the second caption reads FI R 6s.
    Light
  • Illustration of a lighted buoy, which has a red platform, with a rectangular red structure with a square in the upper left side and a white numeral 8 on the upper right. A red light is affixed to the top. Chart mark for lighted buoy, which appears as a magenta circle with a magenta diamond affixed to the upper right side. The first caption reads R "8" and the second caption reads FI R 4s.
    Lighted Buoy
  • Illustration of a nun buoy, which appears as a narrow red cylindrical structure with a tapering top. A red square appears in the upper left, and a white numeral 6 appears on the upper right side. Chart mark for nun buoy, which appears as a clear circle with a magenta diamond shape affixed to the upper right side. The first caption reads R and the second caption reads N "6".
    Nun
  • Illustration of a daybeacon, which appears as a triangle mounted on a pole. The center is red with a dark red border and a red numeral 2 in the center. Chart mark for a daybeacon, which appears as a red triangle. First caption reads R and second caption reads "2".
    Daybeacon

Lateral Aids to Navigation generally indicate which side of an aid to navigation a vessel should pass when channels are entered from seaward. In the absence of a route leading from seaward, the conventional direction of buoyage, generally follows a clockwise direction around landmasses. The most important characteristic of an aid is its color. The "3R" rule "Red Right Returning" is the essential rule of thumb for using the lateral system. This means that when entering one body of water from a larger body of water (i.e. returning to a harbor from a bay or sound), keep the red aids to starboard (right) side and green aids to port (left) side. In addition, each aid is numbered, and these numbers increase as entering from seaward.

Preferred Channel Marks are found at junctions of navigable channels and often mark wrecks or obstructions. A vessel may normally pass this aid on either side, but the top color band indicates the preferred channel. If the top band of the aid is red, it is treated as a red mark and kept to starboard as the vessel passes it while returning from sea. Caution: It may not always be possible to pass on either side of preferred channel aids to navigation. The appropriate nautical chart should always be consulted.

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Non-Lateral Aids to Navigation

Dayboards - May Be Lettered

White SquareWhite Light Only

White Square. Chart mark for dayboard, which appears as a white square. The first caption reads RW and the second caption reads Bn. RW
Bn
Illustration of dayboard, which appears as a diamond with a white border, with two red diamonds vertically and two white diamonds horizontally in the middle. A dark red letter A appears in the upper red diamond.
White Square. Chart mark for dayboard, which appears as a white square. The first caption reads GW and the second caption reads Bn. GW
Bn
Illustration of dayboard, which appears as diamond with a white border, with two green diamonds vertically and two white diamonds horizontally in the middle. A dark green letter A appears in the upper green diamond.
White Square. Chart mark for dayboard, which appears as a white square. The first caption reads BW and the second caption reads Bn. BW
Bn
Illustration of dayboard, which appears as a diamond with a white border, with two black vertical diamonds vertically and two white diamonds horizontally in the middle. A white letter A appears in the upper black diamond.

The sole purpose of these diamond shaped dayboards is to help the vessel operator determine his/her location. They are like the "X's" on shopping mall maps "You Are Here." Appropriate nautical chart must be consulted to determine location.

Safe Water
No Numbers - May Be Lettered

White Square White Light Only   Morse Code
Mo (A) Illustration of Morse code, which shows a sequence of a short flash of white light, a short pause, a medium flash of light and a long pause.
  • Illustration of lighted and/or sound buoy, which has a platform that is white on the left and red on the right. The cylindrical structure is white on the left and red on the white, with a white square on the upper left and a white letter N on the upper right. A white light and a red circle are affixed to the top. Chart mark for lighted and/or sound buoy, which appears as a magenta circle with a clear diamond affixed to the upper right side. A line bisects the diamond vertically and a small clear circle is affixed to the top of the diamond. The first caption reads RW "N" and the second caption reads Mo (A).RW "N" Mo (A)
    Lighted and/or sound
  • Illustration of MR daymark, which appears as an octagon that is white on the left half, red on the right half, and has a white border all around. A white letter A appears in the center of the red half. Chart mark for MR, which appears as a clear square. The first caption reads RW and the second caption reads "A".RW "A"
    MR
  • Illustration of a Can buoy, which appears as a narrow cylinder, which is white on the left side and red on the right side. A white square appears in the upper left and a white letter N appears in the upper right. Chart mark for can buoy, which appears as a clear circle with a clear diamond affixed to the upper right side. A vertical line bisects the diamond. The caption reads RW "N".RW "N"
    Can
  • Illustration of an unlighted and/or sound buoy, which has a platform that is white on the left and red on the right. The rectangular structure is white on the left and red on the right, with a white square on the upper left and a white letter on the upper right. A red circle is affixed to the top. Chart mark for unlighted and/or sound buoy, which appears as a clear circle with a clear diamond affixed to the upper right side. A vertical line bisects the diamond and has a small clear circle affixed to the top. The caption reads RW "N"RW "N"
    Unlighted and/or sound

These aids are used to mark fairways, mid-channels, and offshore approach points, and have unobstructed water on all sides. They can also be used by the vessel operator transiting offshore waters to identify the proximity of intended landfall. Lighted/unlighted buoy may show a red topmark.

Isolated Danger
No Numbers - May Be Lettered

White Square White Light Only
FI(2) 5s   Illustration of flashing white light sequence, which consists of one short flash, a medium pause, a second short flash and a long pause.
  • BR "A" Chart mark for lighted buoy, which consists of a magenta circle with a diamond affixed to the upper right side. The lower half of the diamond is magenta and the upper half is black. Two small black circles appear above the diamond, extending upward diagonally to the right. The first caption reads BR "A" and the second caption reads FI (2) 5s. Illustration of a lighted buoy, which has a black base, a rectangular structure that is red on the bottom and black on top. A white light and two black circles, stacked vertically, are attached to the top. A white letter A appears on the upper right side of the structure.
    Lighted
  • Illustration of an unlighted buoy, which has a black base, and a rectangular structure that is red on the bottom and black on top. Two black circles, stacked vertically, are attached to the top. A white letter C appears on the upper right side of the structure. Chart mark for unlighted buoy, which appears as a clear circle with a diamond affixed to the upper right side. The lower half of the diamond is magetna and the upper half is black. Two small black circles appear above the diamond, extending upward diagonally to the right. The caption reads BR "C".BR "C"
    Unlighted

These aids indicate an isolated danger which may be passed on all sides. They are erected on or moored on or near dangers, they should not be approached closely without special caution.

Range Dayboards - May Be Lettered

  • KGW
    Illustration of KGW range dayboard, which is a rectangle with a white vertical stripe in the middle and a green vertical stripe on either side.
  • KWG
    Illustration of KWG range dayboard, which is a rectangle with a green vertical stripe in the middle and a white vertical stripe on either side.
  • KWB
    Illustration of KWB range dayboard, which is a rectangle with a black vertical stripe in the middle and a white vertical stripe on either side.
  • KBW
    Illustration of KBW range dayboard, which is a rectangle with a white vertical stripe in the middle and a black vertical stripe on either side.
  • KWR
    Illustration of a KWR range dayboard, which is a rectangle with a red vertical stripe in the middle and a white vertical stripe on either side.
  • KRW
    Illustration of a KRW range dayboard, which is a rectangle with a white vertical stripe in the middle and a red vertical stripe on either side.
  • KRB
    Illustration of a KRB range dayboard, which is a rectangle with a black vertical stripe in the middle and a red vertical stripe on either side.
  • KBR
    Illustration of KBR range dayboard, which is a rectangle with a red vertical strip in the middle and a black vertical stripe on either side.
  • KGB
    Illustration of a KGB range dayboard, which is a rectangle with a black vertical stripe in the middle and a green vertical stripe on either side.
  • KBG
    Illustration of a KBG range dayboard, which is a rectangle with a green vertical stripe in the middle and a black vertical stripe on either side.
  • KGR
    Illustration of a KGR range dayboard, which is a rectangle with a red vertical stripe in the middle and a green vertical stripe on either side.
  • KRG
    Illustration of a KRG range dayboard, which is a rectangle with a green vertical stripe in the middle and a red vertical stripe on either side.

Ranges are a PAIR of aids to navigation. When the dayboards and/or lights appear to be in line with each other (Figure "A"), it assists the vessel operator in maintaining a safe course within the navigable channel. The appropriate nautical chart must be consulted when using ranges to determine whether the range marks the centerline of the navigable channel and also what section of the range may be safety traversed. Ranges are generally, but not always, lighted, and display rectangular dayboards of various colors. Ranges which are lit 24 hours a day may not have dayboards.

  • Illustration of a pair of range markers aligned vertically. Each range appears as a rectangle with a green stripe in the middle and a red stripe on either side. A red light appears at the top center of each range. Iso R 6s
    Illustration of a pair of range markers aligned vertically. Each range appears as a rectangle with a green stripe in the middle and a red stripe on either side. A red light appears at the top center of each range. QR
    Figure A

Typical Information and Regulatory Marks

When lighted, may display any light rhythm except quick flashing and flashing (2)

NW   White Square White Light Only

  • Illustration of a danger regulatory mark
  • Illustration of an exclusion area regulatory mark
    Exclusion Area
  • Illustration of a restricted operations regulatory mark
    Restricted Operations
  • Illustration of a danger regulatory mark
    Danger

Information and Regulatory Marks are used to alert vessel operators to various warnings or regulatory matters.

Examples:

  • Illustration of a boat exclusion area daymark, which appears as a white square outlined in orange. A white diamond outlined in orange appears in the center. An orange line bisects the diamond vertically and horizontally. The words "SWIM AREA" appear at the bottom of the square. Boat Exclusion Area
    Explanation may be placed outside the crossed diamond shape, such as dam, rapids, swim area, etc.
  • Illustration of a danger daymark, which appears as a white square outlined in orange. A white diamond outlined in orange appears in the center. The word "ROCK" appears in the center of the diamond. Danger
    The nature of danger may be indicated inside the diamond shape, such as rock, wreck, shoal, dam, etc.
  • Illustration of a controlled area daymark, which appears as a white square outlined in orange. A white circle outlined in orange appears in the middle, with the word "SLOW" inside the circle. The words "NO WAKE" appear at the bottom of the square. Controlled Area
    Type of control is indicated in the circle, such as slow, no wake, anchoring, etc.
  • Illustration of an information daymark, which appears as a white rectangle outlined in orange. The words "MULLET LAKE" appear inside the rectangle, with a long arrow beneath it pointing to the right. The words "BLACK RIVER" appear below the arrow, with a long arrow underneath them pointing to the left. Information
    For displaying information such as directions, distances, locations, etc.
  • Illustration of buoy used to display regulatory markers, which appears as a white cylinder with an orange horizontal stripe on the top and bottom. A white circle outlined in orange appears in the center. The legend "5 MPH" appears inside the circle.
    Buoy used to display regulatory markers.
  • Illustration of buoy used to display regulatory markers, which appears as a white cylinder with an orange horizontal stripe on the top and bottom. A white diamond outlined in orange appears at the center.
    May show white light may be lettered.

Intracoastal Waterway (ICW) Marks

The ICW runs parallel to the Atlantic and gulf coasts from Manasquan Inlet, New Jersey to the Mexican border. Aids to navigation marking the ICW display unique yellow symbols to distinguish them from aids marking other waters. Yellow triangles [yellow square] on your port, regardless of the color navigation aid they appear on.

Examples:

  • Illustration of intercoastal waterway lighted buoy, which has a green platform and green rectangular structure. A green square appears at the top left, a white numeral 5 appears at top right, and a yellow square appears at bottom right. A green light is affixed to the top.
  • Illustration of intercoastal waterway lighted buoy, which has a red platform and red rectangular structure. A red square appears at the top left, a white numeral 6 appears at top right, and a yellow square appears at bottom right. A red light is affixed to the top.
  • Illustration of intercoastal waterway lighted buoy, which has a green platform and green rectangular structure. A green square appears at the top left, a white numeral 7 appears at top right, and a yellow triangle appears at bottom right. A green light is affixed to the top.
  • Illustration of intercoastal waterway lighted buoy, which has a red platform and red rectangular structure. A red square appears at the top left, a white numeral 8 appears at top right, and a yellow triangle appears at bottom right. A red light is affixed to the top.
  • Illustration of an intercoastal waterway can buoy, which is a green rectangular structure with a green square at top left, a white numeral 9 at top right, and a yellow square centered just below the midpoint of the can.
  • Illustration of an intercoastal waterway nun buoy, which is a red rectangle with tapered top. A red square appears at top left, a white numeral 6 appears at top right, and a yellow triangle appears in the center of the nun.
  • Illustration of an intercoastal waterway daybeacon that appears as a green square with a dark green border, mounted on a pole. A yellow triangle is centered in the top of the green square, with a green numeral 3 beneath it.
  • Illustration of an intercoastal waterway daybeacon that appears as a red triangle with a dark red border, mounted on a pole. A yellow triangle is centered at the top of the red triangle and a red numeral 2 appears beneath it.

Mooring Buoy

May Show White or Reflector Light

Illustration of a mooring buoy, which appears as a white cylinder with a blue horizontal stripe across the middle.

Mooring Buoys are white with a blue horizontal band. This distinctive color scheme is used to facilitate identification and to avoid confusion with aids to navigation.

Special Marks - May Be Lettered

yellow square Yellow Light Only

Fixed
Illustration of fixed yellow light, which appears as a continuous beam.
Flashing
Illustration of yellow flashing lights, which appears as a sequence of a short flash followed by a short pause.
  • Illustration of an unlighted can buoy, which appears as a yellow cylinder with a yellow square at top left and a black letter A at top right. Chart mark of an unlighted can buoy, which appears as a clear circle with a clear diamond attached at top right. The first caption reads Y and the second caption reads C "A".
    Unlighted Can
  • Illustration for unlighted nun buoy, which appears as a yellow cylinder with a taped top, with a yellow square at upper left and a black letter C at middle right. Chart mark for unlighted nun buoy, which appears as a clear circle with a clear diamond attached at top right. The first caption reads Y and the second caption reads N "A".
    Unlighted Nun
  • Illustration of a daybeacon, which appears as a yellow diamond with a dark yellow border. A black letter A appears in the center. Chart mark for daybeacon, which appears as a white square. The first caption reads Y "A" and the second caption reads Bn.
    Daybeacon
  • Illustration of a lighted buoy, which has a yellow platform and a yellow rectangular structure with a yellow square at upper left and a black letter B at upper right. A yellow light is attached to the top. Chart mark for lighted buoy, which appears as a magenta circle with a clear diamond attached at the upper right. The first caption reads Y "B" and the second caption reads F1.
    Lighted

These aids are not intended to assist in navigation, but rather to alert the vessel operator to a special feature or area (anchoring, traffic separation, fish net area, cable or pipeline, military exercise areas, jetties, etc.)

Inland (State) Waters Obstruction Mark

May Show White Reflector Or Quick Flashing White Light

Illustration of a state waters obstruction mark, which appears as a cylinder with black and white vertical stripes.

State Water Obstruction Mark is a black/white vertically striped buoy used to indicate to a vessel operator that an obstruction to navigation extends from the nearest shore to the buoy. This means "do not pass between the buoy and the shore." This aid is replacing Cardinal System (buoys) within the USWMS.

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Uniform State Waterway Marking System (USWMS)

Note: The USWMS is presently merging with the U.S. Aids to Navigation System and will be discontinued on December 31, 2003. Vessel operators may encounter both types of systems during this transitional period.

Lateral System

  • May show green reflector or light

    Illustration of solid black buoy, which appears as a black cylinder with a white numeral 3 in the middle.
    Solid Black Buoy

    (Being replaced by Green Can Buoy)
  • Usually found in pairs pass between these buoys
    Port
    Side     — Looking Upstream — Starboard
    Side
  • May show red reflector or light

    Illustration of a solid red buoy, which appears as a red cylinder with a numeral 4 in the center.
    Solid Red Buoy

    (Being replaced by Red Nun Buoy)

Cardinal System

May show white reflector or light

  • Illustration of a red-striped white buoy, which appears as a cylinder with a white top and red and white vertical stripes on the side.
    Red striped white buoy

    Do not pass between buoy and nearest shore
  • Illustration of a black-topped white buoy, which appears as a white cylinder with a black top and a horizontal black band around the top of its sides, and a black numeral 7 in the center.
    Black topped white buoy

    Pass to north or east of buoy
  • Illustration of a red-topped white buoy, which appears as a white cylinder with a red top and a horizontal red band around the top of its sides.
    Red topped white buoy

    Pass to south or west of buoy

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Western Rivers Marking System (As Seen From Seaward)

Port Side
or Right Descending Bank

white square White Lights

Flashing
Illustration of a flashing green light, which appears as a sequence of a short flash followed by a short pause.
ISO
Illustration of a green ISO light, which appears as a sequence of a medium flash followed by a longer pause.
  • Illustration of a light, which appears as a green square with a dark green border, mounted on a pole. A light is attached to the top.
    Light
  • Illustration of a lighted buoy, which has a green platform and green rectangular structure with a green square at upper left. A light is attached to the top.
    Lighted Buoy
  • Illustration of a can buoy, which appears as a green cylinder with a green square at upper left.
    Can
  • Illustration of a passing daybeacon, which appears as a green square with a dark green border, mounted on a pole. A caption at right reads SG.
    Passing Daybeacon
  • Illustration of a crossing daybeacon, which appears as a diamond with two green diamonds inside stacked vertically and two white diamonds stacked horizontally, surrounded by a white border. A caption at right reads CG.
    Crossing Daybeacon
    (May Be Lighted)
  • Illustration of a mile board, which appears as a white rectangle with the black number 176.9 in the center.
    Mile Board (Marker)

Preferred Channel

Mark Junctions and Obstructions Composite Group Flashing (2)

Preferred Channel
to Starboard

Topmost Band Green

FI (2+1) G
Illustration of green flashing light, F1 (2+1) G, which is shown as a sequence of two short flashes separated by a short pause, followed by a medium pause, one more short flash and a long pause.
  • Illustration of a lighted buoy, which has a green platform and a rectangular structure that is green on the top and red on the bottom. A green square appears at upper left and a green light is affixed to the top.
    Lighted Buoy
  • Illustration of a can buoy, which appears as a narrow cylinder that is green on the top, red in the middle, and green on the bottom. A green square appears at upper left.
    Can
  • Illustration of a passing daybeacon, which appears as a square that is red on the bottom, green on top, and surrounded by a corresponding border of dark red and dark green. It is mounted on a pole. A caption to the right reads JG.
    Passing Daybeacon

Preferred Channel
to Port

Topmost Band Red

FI (2+1) R
Illustration of green flashing light, F1 (2+1) R, which is shown as a sequence of two short flashes separated by a short pause, followed by a medium pause, one more short flash and a long pause.
  • Illustration of a lighted buoy, which has a red platform and a rectangular structure that is red on the top and green on the bottom. A red square appears at up left and a red light is affixed to the top.
    Lighted Buoy
  • Illustration of a nun buoy, which appears as a narrow cylinder with a tapered top. The top is red, the middle is green, and the bottom is red. A red square appears at top left.
    Nun
  • Illustration of a passing daybeacon, which appears as a triangle that is green on the bottom, red on top, and surrounded by a corresponding border of dark green and dark red. It is mounted on a pole. A caption to the right reads JR.
    Passing Daybeacon

Starboard Side
or Left Descending Bank

white square White Lights

Flashing (2)
Illustration of a flashing (2) red light, which appears as a sequence of two short flashes separated by a short pause and followed by a longer pause.
ISO
Illustration of a red ISO light, which appears as a sequence of a medium flash followed by a shorter pause.
  • Illustration of a light, which appears as a red triangle with a dark red border, which is attached to a pole. A red light is attached to the top.
    Light
  • Illustration of a lighted buoy, which has a red platform and a red rectangular structure. A red square appears at upper left and a red light is attached to the top.
    Lighted Buoy
  • Illustration of a nun buoy, which appears as a cylindrical red structure with a tapered top. A red square appears at upper left.
    Nun
  • Illustration of a passing daybeacon, which appears as a red triangle surrounded by a dark red border, mounted on a pole. A caption to the side reads TR.
    Passing Daybeacon
  • Illustration of a crossing daybeacon, which appears as a diamond with two red diamonds inside stacked vertically and two white diamonds stacked horizontally, surrounded by a white border. A caption at right reads CR.
    Crossing Daybeacon
    (May Be Lighted)
  • Illustration of a mile board, which appears as a white rectangle with the black number 123.5 in the center.
    Mile Board (Marker)

Western Rivers Marking System is a variation of the standard U.S. Aids to Navigation System (ATONS) and is found on the Mississippi River and tributaries above Baton Rouge, and on certain other rivers which flow toward the Gulf of Mexico. Red daybeacons, lights, and buoys mark the starboard banks and limits of channels as vessels "return for sea" or proceed upstream. Green daybeacons, lights, and buoys mark the port banks and limits of navigable channels while going upstream. The Western River System varies of the standard U.S. system as follows:

  1. Buoys are not numbered.
  2. Passing daybeacons are not numbered but normally have an attached "Mile Marker" board that indicates the distance in statute miles from a fixed point (normally the river mouth).
  3. Diamond-shaped non-lateral dayboards checkered red-and-white or green-and-white, similar to those used in the U.S. Aids to Navigation System, are used as Crossing daybeacons where the river channel crosses from one bank to the other.
  4. Lights on green buoys and on beacons with green daymarks show a single flash, which may be green or white.
  5. Lights on red buoys and on beacons with red daymarks show a double flash [Group Flashing (2)], which may be red or white.
  6. Isolated danger marks and Safe water marks are not used.

River Bank Names: When traveling downstream the banks are named "right" and "left". The right bank has green aids and the left bank has red aids, thus the west bank of the Mississippi is its right bank and it has green aids. To avoid confusion, commercial river traffic often calls the right bank the right descending bank and the left bank the left descending bank, expressed in this way, leaves no room for doubt.

Mile Markers: These markers are some of the most useful aids on a river. They are attached to daybeacons or displayed in other easily seen places. Since the U.S. Corps of Engineers erects them, they show distance in statute miles rather than nautical miles. With the exception of the Ohio River, mile markers indicate the distance up stream from the mouth of a river. Ohio River markers start at its headwaters and indicate the distance downstream. Mile Markers also help a vessel operator locate his/her position on a river chart.

Crossing daybeacons: Because the navigable channels of rivers swing from bank to bank as the river bends, diamond-shaped crossing daybeacons are used to assist river traffic by indicating where the channel has changed from one side of the river to the other. Crossing daybeacons are always on the opposite side of the river. When a diamond-shaped crossing daybeacon is sighted, the vessel operator should head for the "diamond", and treat the color of the daybeacon as a channel mark (i.e. red mark keep to the left bank when traveling downstream).

River Buoys: Changes in river channels caused by fluctuations in water level, current speed and shifting shoals make buoys maintenance a continuous task for the Coast Guard. In wintertime where rivers freeze, buoys are lost or moved from position. Because of their somewhat temporary nature, river buoys do not have letters or numbers and are not usually shown on river charts.

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Visual Buoyage Guide

Illustration of a water way area with the preferred channel (marked by a sold black line and arrow) going slightly left, a secondary channel (marked by a dotted black line and arrow) going right, and an intercoastal waterway (marked by a solid magenta line) going across the area horizontally.

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Nautical Chart (Fictitious)

Illustration that depicts the preferred channel going through a water area that corresponds to the area shown in the visual buoyage guide, letting a person compare the navigational aids depicted with the corresponding chart marks.

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Bridge Lighting and Other Signals

Bridge Lighting: In U.S. waters, the Coast Guard prescribes certain combinations of fixed lights for bridges and structures extending over waterways. In general, red lights (A) are used to mark piers and supports, and green lights (B) mark the centerline of the navigable channel through a fixed bridge. If there is more than one channel through the bridge, the preferred route is marked by three white lights (C) placed vertically. Red lights (D) are also used on some lift bridges to indicate the lift is closed, and green lights (E) to indicate that the lift is open to vessel traffic. Double-opening swing bridges are lighted with three lanterns on top of the span structure so that when viewed from an approaching vessel the swing span when closed will display three red lights (F), and when open for navigation will display two green lights (G).

  • Illustration of lighting on a fixed bridge over a main channel. A red light is affixed towards the main support pier on each side of the central span. A green light is affixed to the center of the span. A series of three vertical white lights is affixed to the center of the span.
    Fixed Bridge
  • Illustration of lighting on a double leaf (lift) bascule bridge. In the closed position, two red lights are affixed to each pier on either side of the main span and two additional red lights are affixed to the center of the span. In the open position a single green light is attached to each side of the open, raised bridge span.
    Double Leaf (Lift) Bascule Bridge
  • Illustration of lighting on a vertical lift span bridge that is open. Two red lights are attached at the base of the support piers on either side of the main span. A single green light is affixed to the center of the span.
    Vertical Lift Span Bridge (Open)
  • Illustration of lighting on a vertical lift span bridge that is closed. Two red lights are affixed near the bottom of each support pier. An additional red light is affixed to the bottom center of the span.
    Vertical Lift Span Bridge (Closed)
  • Illustration of lighting on a double opening swing bridge that is open. Two red lights are affixed to the support piers on either side of the main span and three red lights are affixed to the central support pier. Two green lights are affixed in a vertical arrangement on the central raised part of the span.
    Double Opening Swing Bridge (Open)
  • Illustration of lighting on a double-opening swing bridge that is closed. Two red lights are affixed to the end support piers and three red lights are affixed to the central support pier. A single red light is affixed to the top of the highest portion of the bridge span, while an additional red light is affixed to the second highest points on either side.
    Double Opening Swing Bridge (Closed)

Clearance Gauges are extremely valuable to vessel operators because they indicate the vertical distance (clearance) between the "low steel" of the bridge channel span and the waterline (They do not indicate the depth of water under the bridge). These gauges are permanently fixed to the bridge pier or structure and located on the right side of the channel facing approaching vessels. Each gauge is marked by black numbers and foot marks (lines) on a white background board. The picture to the right illustrates a clearance of approximately 7 feet 9 inches, since the 8-foot mark line is not visible.

Photograph of a clearance gauge affixed to a bridge pier. The gauge indicates a clearance of 8 feet. Clearence Gauge

Drawbridge Opening Signals: The operator of a vessel requesting a drawbridge to open shall signal the bridge tender, and the bridge tender shall acknowledge that signal. The following are the mnost common types of signals a vessel operator should use to request an opening:

  1. Radiotelephone Communications - Most bridges monitor VHF-FM channels 13 and 16 with the exception of bridges in Florida. In June 1996, the FCC published a notice stating that all boaters throughout the State of Florida should hail bridge tenders on VHF-FM channel 9 to reduce the high amount of traffic on channel 13. Boaters operating in Georgia and South Carolina are encouraged to follow the same procedures.
    Note: Boaters should always use "low power (1watt) output" on their VHF-FM marine radio when hailing a bridge tender.
  2. Sound Signals - These signals shall be made by whistle, horn, megaphone, or hailer. To request an opening, the vessel operator shall give the "opening signal" consisting of one prolonged blast (4 to 6 seconds duration) followed by one short blast (about 1 second duration). The draw tender shall reply with the same sound signal (one prolonged followed by one short) acknowledging that the draw can be opened immediately. When a vessel approaches a drawbridge with the draw in the open position, the vessel shall give the opening signal. If no acknowledgement is received within 30 seconds, the vessel may proceed, with caution, through the open draw. When a draw cannot be opened immediately, or is open and must be closed promptly, the draw tender shall give five short blasts sounded in rapid succession after the vessel's opening signal request.

Further information on drawbridge regulations and opening signals for bridges over the Navigable Waterway can be found in the U.S. Coast Pilots.

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Aids To Navigation Abbreviations

  • B - Black
  • Bn - Beacon
  • C - Can Buoy
  • F - Fixed
  • Fl - Flashing
  • Fl (2) - Group Flashing
  • Fl (2+1) - Composite Group-Flashing
  • G - Green
  • Iso - Isophase
  • J - Junction (S or T Dayboard)
  • K - Rectangular (Range Dayboard)
  • M - Safe Water (Octagonal)
  • MO (A) - Morse Code
  • N - Nun Buoy
  • Oc - Occulting
  • Pri - Private
  • Q - Quick (Flashing)
  • R - Red
  • S - Square Dayboard
  • s - seconds
  • T - Triangle Dayboard
  • W - White
  • Y - Yellow

A Complete listing of Nautical Chart symbols, abbreviations and terms is contained in Chart No.1 publication. This publication is available at most marine stores.

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Coast Guard District Aids To Navigation Offices

District Phone # Waters of Jurisdiction
First 616-223-8338 ME, NH, VT (Lake Champlain) RI, CT, MA and NY to Shrewsbury River, NJ.
Fifth 757-398-6486 Shrewsbury, NJ to DE, MD, PA, VA, DC & NC.
Seventh 305-415-6730 SC, GA, FL to 83 ∞ 50'W, Puerto Rico & adjacent islands of the U.S.
Eighth 504-589-6277 Fl westward from 83 ∞ 50'W, AL MS, LA, TX, the Mississippi River System except that portion of the Illinois River north of Joliet, IL.
Ninth 216-902-6060 Great Lakes and St. Lawrence River above St. Regis River.
Eleventh 510-437-2976 CA
Thirteenth 206-220-7270 OR, WA, ID and MT.
Fourteenth 804-541-2315 HI, American Samoa, Marshall, Marianas, & Islands
Seventeenth 907-463-2262 AK

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Report Aids To Navigation Defects to the Coast Guard

TAKE TIME TO REFLECT ON SAFETY . . . SAFE BOATING BEGINS WITH YOU!

Boaters need to realize the Coast Guard cannot keep the thousands of aids to navigation comprising the U.S. Aids to Navigation System under continual observation. It is impossible to maintain every aid to navigation at all times. Therefore, for the safety of all boaters, if you discover that an Aid to Navigation is:

  • missing
  • damaged
  • moved from its original position
  • displaying an improper signal (light color or timing incorrect, sound signal not functioning)
  • a hazard to navigation

Report this information by radio or phone to the nearest Coast Guard Unit or Coast Guard District Aids To Navigation Office.

ALL AIDS TO NAVIGATION ARE PROTECTED BY LAW

It's a criminal offense to cause any damage or hindrance to the proper operation of any aid.

Do not alter, deface, move or destroy any aid to navigation. Never tie a vessel to a buoy, daybeacon or light structure.

Avoid anchoring so close to an aid that the aid is obstructed(hidden) from sight of another vessel.

Report all intentional or unintentional collisions with navigation aids to the U.S. Coast Guard.

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