www.uscgboating.org 1 U.S. Aids to Navigation System

What You Need to Know About the Markers on the Water

A Handy Guide from the United States Coast Guard
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

1 2 U.S. Aids to Navigation System

Aids to Navigation can provide a boater with information similar to 

that which drivers get from street signs, stop signals, road barriers, detours, and traffic lights.

This booklet will give you, the recreational boater, the basic 

information you need about the U.S. Aids to Navigation System 

(USATONS). This information will help you recognize, understand, and 

navigate by the colors, shapes, numbers, and lights you will encounter on 

the water. It will also give you the basic tools you need to read a nautical chart. 

In addition, you will find information on safety, the proper way to interact with other vessels, tips on boating at night, and how to handle special situations you might encounter, 

like bridges and locks.

Take some time to review this booklet, and keep it onboard your boat as a quick reference. Your understanding of the markers you see on the water will help ensure that you, 

your family, and your friends have fun – and safe – boating trips.

 Best Regards,

 United States Coast Guard Boating Safety Division

STOP Read This Booklet. Stay Safe on the Water.

AIDS TO 

NAVIGATION ARE

THE WATERWAYS’ 

ROAD SIGNS

Most boating accidents are preventable! Be sure to:

Boaters call navigation rules – the basic laws governing the steering or sailing of a boat – 

“The Rules of the Road.” The Rules of the Road define the roles and responsibilities of 

vessel operators. If all operators obeyed these rules, most accidents could be avoided. 

One of the reasons the Rules of the Road exist is to keep boats 

from colliding with each other and with other objects. Since 

collisions are the number one type of accident on the water, 

boaters should remember the following Rules of the Road.

Post a lookout. Designate someone to watch for dangers 

that may come from any direction. 

Maintain a safe speed. Except where speed is restricted 

by regulation or the waterway is marked by a “No Wake” 

or “Slow Speed” Aid, you must judge “safe speed” for 

yourself, taking into account visibility, vessel traffic, your boat’s ability to 

maneuver, and the weather conditions.

Avoid a collision. The Rules of the Road include the actions to take when encountering 

another vessel on the water. Some of the most common situations you may encounter 

are: overtaking, meeting head on, and crossing the bow of another vessel. In each 

case, the boat designated as the “give-way” vessel is required to yield to the other 

boat, while the boat designated as the “stand-on” vessel should maintain its course 

and speed.

The Rules vary slightly depending on whether you are 

boating on inland or on international waters. As an 

example, when operating on inland waters, sound signals 

are signals of intent; when operating on international 

waters, they are signals of action.

•	 Always wear your life jacket and require the

same of your passengers

•	 Never boat under the influence

•	 Take a boating safety course

•	 Get a free Vessel Safety Check

Introduction 1. Navigation Rules (Rules of the Road)
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

3 4 U.S. Aids to Navigation System

2 short blasts

(1 sec.each)

1 short blast

(1 sec.each)

2 short blasts

(1 sec.each)

1 short blast

(1 sec.each)

Stand-on Vessel

Overtaken

Give-way Vessel

Overtaking

(keep clear)

Overtaking Situation (Navigation Rule 13) Head-On Situation (Navigation Rule 14)

Port-to-Port Passing (preferred)

Action(s): The give-way vessel (bottom) can pass on either side of the stand-on 

vessel (top). 

Sound signals, inland: Passing portside requires two short (1-second) blasts on the horn 

signaling the overtaking boat’s intention, and two short blasts for the stand-on vessel’s 

agreement. Passing to starboard requires one short blast for intent and agreement.

Sound signals, international: Passing portside requires two prolonged (4-6 seconds) 

and two short blasts for the overtaking boat’s intention, two short blasts for the stand-on 

vessel’s agreement. Passing to starboard requires two prolonged and one short blast for 

intention. An agreement signal is only required when operating 

in a narrow channel or fairway; then the following blast pattern 

signals your agreement: one prolonged/one short/one 

prolonged/one short. 

1 short blast (1 sec.) 1 short blast (1 sec.)

Action(s): When meeting another vessel head on, a port-to-port passing is preferred. 

Passing starboard-to-starboard is acceptable when necessary. 

Sound signals: Passing port-to-port requires one short horn blast to signal intention and 

one short blast for agreement. Passing to starboard requires two short blasts from each 

vessel.

2 short blasts

(1 sec. each)

2 short blasts

(1 sec. each)

1 short blast

(1 sec.)

1 short blast (1 sec.)

2 short blasts (1 sec. each) 2 short blasts (1 sec. each)

1 short blast (1 sec.)

1 short blast

(1 sec.)

Stand-On Vessel

Overtaken

Give-Way Vessel

Overtaking

(keep clear)

Starboard-to-Starboard Passing
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

5 6 U.S. Aids to Navigation System

Crossing Situation (Navigation Rule 15)

Action(s): In a crossing situation, 

the give-way vessel must act to 

avoid a collision. This may include 

altering its course to pass astern 

of the stand-on vessel or slowing 

down. The stand-on vessel should 

maintain its course and speed. 

Sound signals, inland: The give-way vessel signals the stand-on vessel with one short 

horn blast. The stand-on vessel agrees with one short horn blast. 

Sound signals, international: The give-way vessel signals the stand-on vessel with one 

short horn blast. No agreement signal by the stand-on vessel is required.

There is much more to the Navigation Rules than can be covered here. For more 

information, go to www.uscgboating.org or www.navcen.uscg.gov.

When meeting another boat, make early and substantial changes to your course. 

This helps the other operator understand your intentions.

The two main types of Aids to Navigation 

are buoys and beacons.

Buoys are Aids that float on top of the 

water, but are moored to the bottom of the 

body of water. Some have a light affixed to 

the top; some do not. A buoy with a cylindrical shape and a conical top is referred to 

as a “nun.” A buoy with a cylindrical shape 

and a flat top is called a “can.”

Beacons are Aids that are permanently 

fixed, most commonly to the bottom of a 

body of water. A beacon that has a light 

attached is simply referred to as a “light”; 

a beacon without a light attached is called 

a “daybeacon.”

Both buoys and beacons can provide 

a variety of navigation information via 

shape, color, light, and/or audible signal. 

Dayboards are informational signboards.

The term topmark refers to a non-lighting 

element, such as a sphere, that may be 

affixed to the top of an Aid.

2. The Essential Markers: On the Water and On the Charts

R "2A"

G

C "5A"

FI R 4s

30ft 6M "4"

RG

N "CF"

R "4"

Q R

FI G 4s 15ft 5M "5"

RED LIGHTED BUOY

Red: always even numbers

RED LIGHT

GREEN CAN BUOY

Green: always odd numbers

GREEN LIGHT

RED/GREEN NUN BUOY

RED DAYBEACON

Give-Way Vessel

should alter course to 

pass astern (behind)

1 short blast (1 sec.)

Stand-On Vessel

should maintain its 

course and speed

1 short blast (1 sec.)
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

7 8 U.S. Aids to Navigation System

Understanding the Symbols in This Booklet

Buoys, beacons, and all other Aids have a corresponding symbol used on nautical 

charts. In this booklet, you will see representations of Aids, each alongside its nautical 

chart symbol: 

Nautical Charts

It is critical to know where you are going, what routes 

to take, and which areas to avoid before you begin 

your boating trip. Nautical charts are the boating 

equivalent of road maps. A nautical chart provides 

boaters with an aerial view of a waterway with its 

Aids to Navigation, landmarks, and bridges, as well 

as information on water depth, latitude and longitude, and a variety of other important navigational 

information. 

Nautical chart 

symbol

Nautical chart 

abbreviation

Indication of lighted Aid*

Letter* (B)

Flash Period* (6 seconds)

Light color* (red)

Aid type

Aid color (red-green)

* Not on all Aids

Aid color (red-green)

Light characteristic*

(composite group 

flashing)

RG “B”

FI (2+1) R 6s

•	 Always use a current navigation chart and be sure to check www.navcen.uscg.gov for

any relevant Notices to Mariners before your trip.

•	 While electronic chart systems (ECS) can provide boaters with excellent information,

keep relevant paper charts on board. Should your ECS or GPS malfunction, you will 

be very glad to have a backup. 

•	 Remember that most accidents are caused by human error. Do not let an electronic

navigation device take the place of knowing and adhering to the Navigation Rules. 

What You See Depends on Where You Boat

The Aids to Navigation system used on the majority of American waterways is referred to 

as the U.S. Aids to Navigation System or IALA-B. A description of USATONS follows. 

The Mississippi River and its tributaries follow a variation of USATONS called the Western 

Rivers Marking System. An explanation of this system begins on page 23. 

The system used exclusively on the Intracoastal Waterway, which runs along the United 

States coast from New Jersey through Texas, is described beginning on page 25. 

Another system, called the Uniform State Waterway Marking System, has mostly been 

phased out. However, these Aids are shown on page 26 as you may occasionally encounter them.

There are also private Aids to Navigation, which are Aids that are neither owned nor 

maintained by the U.S. Coast Guard. These typically look similar to those in the 

systems described in this booklet and are represented by the same nautical chart 

symbols, with the addition of “Priv,” or “Priv maintd.”

B

B

Retro-reflective 

panel*

Light*

Letter

Aid

RG “B”

FI (2+1) R 6s

Lighted Buoy

Lighted Buoy
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

9 10 U.S. Aids to Navigation System

Lateral Aids to Navigation

Lateral Aids to Navigation are generally used for well-defined channels to indicate the 

route to be followed. These Aids show the sides of a navigable channel, mark junctions 

and forks or splits in the channel, indicate the safe side to pass a hazard to navigation, 

and mark the safe centerline on wide bodies of water. 

They are used in conjunction with a conventional direction of buoyage (a local direction 

of buoyage when approaching a harbor, river estuary, or other waterway from seaward).

“Red, Right, Returning”

You may have heard the phrase, “Red, Right, Returning.” This expression refers to the 

fact that when returning (entering a channel from the open sea or proceeding upstream), 

a boater must keep the red Aids on the right (starboard) side of the boat. These Aids 

have even numbers, and the numbers should increase as you proceed inland. 

When proceeding toward open water (seaward), navigate so that the green Aids are 

to starboard. In this instance, you will see odd numbers on the Aids and the numbers 

should decrease as you proceed toward open water (seaward).

If there is no route marked, navigate clockwise around landmasses.

1

Green colors and 

lights should be 

on your right 

(starboard) side 

when traveling 

toward open waters

(seaward)

2 1 1 2

open water

open water channel

channel

channel

channel

7

5

3

1

8

6

4

Green Aids: Odd Numbers

Square dayboards, buoys, and

cans

Proceeding Upstream

Open Water

(seaward)

Red Aids: Even Numbers

Red, Right, Returning: when 

proceeding upstream, keep the 

red Aids to starboard

Daybeacon

G

“7”

R

“8” Daybeacon

Can

G

C “3”

R

N “4” Nun

Lighted Buoy

G “1”

FI G 4s

R “2”

FI R 4s Lighted Buoy

Light

“5”

FI G 6s

“6”

FI R 6s Light

Characteristics

•	 Beacons may have green odd numbers.

•	 Buoys may have white odd numbers.

•	 If lit, the light will be green and is likely to flash in one

of the following patterns:

Flashing (2)

Flashing

Occulting

Quick Flashing

Isophase

Flashing (2)

Flashing

Occulting

Quick Flashing

Isophase

Characteristics

•	 Beacons may have red even numbers.

•	 Buoys may have white even numbers.

•	 If lit, the light will be red and is likely to flash in one of

the following patterns:

(see page 22 for more on lights)

2

2

Red colors and 

lights should be 

on your right 

(starboard) side 

when traveling 

from open waters 

(shoreward)

3. U.S. Aids to Navigation System (IALA-B)
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

11 12 U.S. Aids to Navigation System

Daybeacon

Can Buoy

Daybeacon

Nun Buoy

GR

“U”

RG

“G”

GR

C “S”

RG

N “C”

GR “A”

FI (2+1) G 6s

RG “B”

FI (2+1) R 6s

Preferred-Channel Aids

Beacons and buoys that have horizontal bands of both red and 

green mark the junction of navigable channels. The top-most color 

indicates the direction of the preferred, or primary, channel. 

When returning (entering a channel from the open sea or proceeding upstream), keeping the Aids with red as the top-most color on the right (starboard) 

side of the boat will place the boater in the preferred channel, while keeping those 

Aids on the port side will place the boater in the secondary channel. When proceeding 

toward open water (seaward), keeping the Aids with green as the top-most color on the 

right (starboard) side of the boat will place the boater in the preferred channel, while 

keeping those Aids on the port side will place the boater in the secondary channel. 

Characteristics

•	 Green on top.

•	 Have a letter designation.

•	 Buoys will feature a white letter.

•	 If lit:

Characteristics

•	 Red on top.

•	 Have a letter designation.

•	 Buoys will feature a white letter.

•	 If lit:

Characteristics

•	 White with red, green, or black diamonds.

•	 Usually lettered (the letter can be matched to a nautical chart to check position).

•	 In the illustrations above,“NR,”“NG,” and “NB”indicate non-lateral red, green, and black. The chart U symbol is to the lower right of each illustration (e.g., “RW Bn” indicates a red-and-white beacon).

S

A

G

C

B

Lighted Buoy Lighted Buoy

COMPOSITE GROUP 

FLASHING (2+1)

COMPOSITE GROUP 

FLASHING (2+1)

(see page 22 for more on lights)

Non-Lateral Aids to Navigation

Non-lateral Aids are the on-the-water versions of the informational, regulatory, and 

warning signs encountered on the road.

Diamond-Shaped Dayboards

Diamond shaped dayboards are used to help determine location. They are the nautical 

equivalent of “You Are Here” markers. An appropriate nautical chart must be consulted 

to determine your exact position.

N

A G

N

N

RW “N”

Unlighted 

with or w/o 

sound

N

A G

N

MR

RW “A”

N

A G

N

Spherical

SP “G”

N

A G

N

Can

RW “N”

N

A G

N

N

RW “N”

Mo (A)

RW

Bn

NR

GW “A”

Bn

NG

BW “M”

Bn

NB

A M

Characteristics

•	 White and red vertical stripes.

•	 A variety of shapes.

•	 May be lettered.

•	 Buoy may have red topmark.

•	 If lit:

(Morse Code “A”)

Preferred 

Channel

Safe Water Marks

These Aids are used to mark fairways, mid-channels, and offshore approach points. 

They have unobstructed water on all sides. A buoy, lighted or unlighted, may show a red 

topmark. An appropriate nautical chart must be consulted to determine exact position.

Lighted 

with or w/o 

sound
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

13 14 U.S. Aids to Navigation System

Isolated Danger Marks

These Aids indicate an isolated danger that may be passed on all sides. Use caution 

when approaching.

A C BR “A”

FI (2) 5s

Lighted

BR “C”

Unlighted

Characteristics

•	 Rectangular with two colors arranged as three vertical

stripes.

•	 May be lettered.

•	 When lit, rear light will be higher then the front light.

•	 Light characteristics may vary; usually the rear (upper)

light remains lit (fixed), while the front (lower) light flashes.

Characteristics

•	 Buoy with black and red horizontal

bands.

•	 May be lettered.

•	 Black double-sphere topmark.

•	 If lit: FI (2) 5s

Range Dayboards

These Aids, which are usually shore-mounted, come in pairs to help the vessel operator 

maintain a straight and safe course within a navigable channel. Each member of the 

pair is separated from the next in 

distance and elevation, with the one 

in front shorter than the one behind it. 

When the two appear to be vertically 

stacked, the vessel is on the range 

line.

Rear light

Front light

Side View

Front View

Left of 

range line

Right of 

range line

On range 

line

When the front (bottom) marker is 

to the right of the rear (top) one, 

you are to the left of the range. 

You should turn right (starboard) 

to get onto the range line.

When the front (bottom) marker 

is to the left of the rear (top) 

one, you are to the right of the 

range. You should turn left 

(port) to get onto the range line.

The two range markers 

are in line, which 

indicates you are on 

the range line.

Front 

marker

Front 

marker

Front 

marker

Front marker Front marker Front marker

Rear marker Rear marker Rear marker

Rear marker Rear marker Rear marker

The colors of range dayboards do not impact navigation – colors are simply 

chosen based on how well they stand out from the background scenery. 

Some combinations:

KGW KWG KBW KWB KWR KRW KRB KBR KGB KBG KGR KRG

Iso R 1 QR
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

15 16 U.S. Aids to Navigation System

Information and Regulatory Marks

These orange-and-white Aids are used to alert vessel operators to various warnings and 

regulations. 

Information

Marks with a square 

provide helpful 

information such as 

directions, distances, 

and locations

Restricted 

Operations

Marks with a circle 

indicate areas with 

regulated operations

Danger

A diamond shape 

alerts boaters to 

hazards

Exclusion

A diamond shape 

with a cross means 

boats are prohibited 

from the area

Symbol

DANGER

GAS

DOCK

BOAT

RAMP

NO WAKE

IDLE SPEED

BOATS

KEEP OUT

SWIM AREA

ROCK

mph

5

Meaning Examples

Characteristics

•	 White with an orange horizontal band at both top and bottom.

•	 Black text within or around an orange square, circle, or diamond;

or black text outside a diamond with an orange cross.

•	 May be buoys or beacons.

•	 If lit, the light will be white and may have any light rhythm except

quick flashing, flashing (2), or Morse code “A.”

•	 The chart symbol for this type of buoy is:

Characteristics

•	 All-yellow.

•	 Come in a variety of shapes.

•	 May have one black letter.

•	 If lit:

Characteristics

•	 White with blue horizontal band.

•	 Cylinder and sphere shapes.

•	 May show a white reflector or display white or yellow light.

Characteristics

•	 Black-and-white vertically striped buoy.

•	 May show a white reflector or display a quick-flashing white light.

Special Aids

These Aids indicate special areas or features such as anchoring, traffic separation, 

fishnet area, cables or pipelines, military exercise areas, and jetties. 

Mooring Buoys

While not a navigational Aid, mooring buoys are 

worth mentioning. They are the only type of buoys 

to which mooring is permitted. Most mooring 

buoys are privately owned or are rental buoys. 

Permission is usually needed to use them. 

State Waters Obstruction Mark

The State Water Obstruction Mark indicates to a 

vessel operator that an obstruction to navigation 

extends from the nearest shore to the buoy. Do not 

pass between the buoy and the shore.

A C

A

B Y

C “A”

Y

N “C” Y “B”

FI Y

Y “A”

Bn

Unlighted Lighted

or

W Or
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

17 18 U.S. Aids to Navigation System 3 1 1 5 3 2 2 4 2 8 6 4 1 3 5 7 2 2

Visual Buoyage Guide Example

Nautical Chart Example

Preferred Channel 

Secondary Channel 

Intracoastal Waterway

“1”

FI (2) G 6s

RG

FI (2+1) R 6s

R “2”

FI R 6s

R “4”

Oc R 6s

G “3”

FI G 6s

G “1”

Iso G 4s

BR “C”

FI (2) 5s

G “5”

F

G “7”

F

I (2) G 6s

I G 4s

R “4”

G “5” R “6”

FI (2) R 6s

R “8”

FI R 4s

RW

Mo (A)

“2”

Iso R 6s

Iso R 6s

QR

“1”

Iso G 4s

“2”

FI R 4s

R

N “2”

G “3”

R “2”

RW

Bn

G

C “3”

(fictitious; same circumstances as above)

(fictitious)
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

19 20 U.S. Aids to Navigation System

Boating at night can make even familiar waters unrecognizable. Visual depth perception 

is lessened and lights from the shore can be difficult to distinguish from those on the 

water. To make nighttime boating safer, keep the following in mind. 

Navigation Lights

Vessels are required to show navigation lights from sunset to sunrise and during periods 

of restricted visibility. Understanding these light displays will provide invaluable information to the boater, as these lights can help the boater determine the length of another 

vessel, its orientation in relation to 

your boat, and the general direction in 

which it is headed. All operators must 

ensure that their vessel’s navigation 

lights are working and that the positioning and distance from which they 

can be seen meet federal regulations. 

It is important to know which navigation lights you will see from another 

boat in certain situations. This can help you determine if you are in an overtaking, meeting, or crossing situation. The following chart illustrates the navigation lights you will see 

from various angles: 

Whenever you see a red navigation light from another vessel, give way. It is the standon vessel. According to the Rules of the Road, it has the right of way (see page 2).

If you see both the red and green sidelights of another boat, it is coming straight 

toward you. You should take action to change course in order to avoid a collision. 

Starboard Bow Stern Port Side

Keep in Mind

•	 It is risky to rely on memory or to take shortcuts at night. Stick to the main channel. 

Your best bet is to navigate by the appropriate chart and identify the corresponding 

Aids to Navigation. 

•	 Make sure you are familiar with the handling characteristics of your boat so you can

concentrate on interpreting the Aids to Navigation.

•	 Slow down. Distances are more difficult to judge at night and you will need more

time to distinguish the various types of lights you will see: navigation lights, lights 

from Aids, and lights on shore.

•	 Listen. You might hear certain sounds before you see the related objects or situations that require you to change course, such as another boat’s engine or sound 

signals, an Aid’s bell or gong, or noises from shore. (Note that sound travels far over 

water.)

•	 Turn on your navigation lights from sunset to sunrise and during daytime periods of

reduced visibility, such as rain and fog.

•	 Turn off any lights that might interfere with, or be confused with, navigation lights.

Temporary image

4. Boating at Night
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

21 22 U.S. Aids to Navigation System

Nighttime Buoyage Guide Example

=

(fictitious; same circumstances as pages 17-18)

The various combinations of these characteristics enable boaters to tell one Aid from 

another in darkness. The following shows how common light display characteristics are 

illustrated and how they operate:

Chart

Abbreviation Type/Description

F Fixed

Shines continuously and steadily; no dark phase.

Fl Flashing

The light goes on at regular intervals; the duration 

of the light phases are less than the duration of 

the dark phases.

Fl (2) Group Flashing

Groups of two flashes that are repeated several 

times a minute.

Fl (2+1) Composite Group Flashing

A group of two flashes followed by a single flash, 

the entirety repeated several times a minute.

Iso Isophase

All durations of light and dark are equal.

Mo (A) Morse Code

Short (“dots”) and long (“dashes”) flashes of light 

are used to represent Morse code; usually flashes 

the letter “A.”

Oc Occulting

The light goes on at regular intervals; the duration 

of the light phases is greater than the duration of 

the dark phases.

Q Quick (Flashing)

Very rapid flashing (more than 60 flashes a minute).

Illustration

Aids to Navigation at Night

At night, Aids to Navigation can only be identified by their light characteristics: 

• Color (red , green , white , or yellow ).

• Light display (sequence of flashes).

• Period (time it takes to go through one sequence of flashes).

• Equipped with retroreflective material.
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

23 24 U.S. Aids to Navigation System

• Crossing daybeacons are used to assist river traffic by indicating where the channel has changed from one side of the river to the other; the aid that marks this 

channel change will be on the opposite side of the river. When encountered, a 

vessel operator should head for the Aid, using its color as a channel mark.

•	 Isolated danger marks and safe-water marks are not used.

•	 River banks are named based on their downstream direction: either “left bank” and “right bank” or “left descending 

bank” and “right descending bank.”

•	 Because of their somewhat temporary nature,Western River

buoys do not have numbers or letters and are not always 

marked on river charts because they tend to drift due to 

fluctuating water level, current speed, and shifting shoals.

Characteristics

If lit, the light will be green 

and will flash as:

Flashing

 FI (2+1) G

Characteristics

If lit, the light will be red 

and will flash as: 

Flashing

 FI (2+1) R

Upstream

Downstream

Lighted buoy Lighted buoy

Can Nun

Daybeacon Daybeacon

Preferred-Channel Aids

Western Rivers Marking System

When on the Mississippi River, tributaries above Baton Rouge, and several other rivers 

that flow toward the Gulf of Mexico, boaters must follow a system called the Western 

Rivers Marking System, a variation of the U.S. Aids to Navigation System.

Upstream (proceeding inland)

Port Side/

Right Descending Bank

Starboard Side/

Left Descending Bank

Downstream (proceeding to Gulf of Mexico)

Characteristics

If lit, the light will be green or 

white and may flash as:

Flashing

Isophase 

Characteristics

If lit, the light will be red or 

white and may flash as: 

Flashing (2)

Isophase

In the Western Rivers Marking System:

• Buoys are not numbered.

•	 Beacons are not numbered, but normally have a mile marker that indicates the

distance in statute miles from a fixed point, typically the river’s mouth.

Port and Starboard Aids

5. Aids to Navigation Systems
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

25 26 U.S. Aids to Navigation System

3 4

7

Uniform State Waterway Marking System 

The Uniform State Waterway Marking System (USWMS) was discontinued and replaced 

by the U.S. Aids to Navigation System (USATONS) in 2003. Should you come across 

one that has not yet been replaced, a guide is provided below:

3 4

7

3 4

Acts as the green 

can buoy in 

USATONS

Acts as the red 

nun buoy in 

USATONS

South or West North or East

Lateral System – USWMS

Cardinal System – USWMS

Cardinal buoys serve as the USWMS version of USATONS’ preferred-channel markers, 

as they indicate the primary route. They are named “cardinal” buoys after the cardinal 

points (north, south, east, and west) of the compass:

3 4

7

3 4

7

The USMWS system’s redand-white vertically striped 

buoy means obstruction. 

In USATONS, a red-andwhite vertically striped buoy 

means safe water.

Larger

Body of Water

Smaller 

Body of Water

Intracoastal Waterway 

The Intracoastal Waterway (ICW) runs just inland and parallel to the Atlantic and Gulf 

coasts from Manasquan, New Jersey to the Mexican border. The Aids to Navigation of 

the ICW closely resemble the green and red buoys and beacons of the lateral system 

previously discussed.

When operating in the ICW, the color of the Aids will typically correspond to the 

USATONS scheme (Red, Right, Returning). The yellow squares, triangles, and bands 

attached to the Aids are the primary ICW indicators. Boaters need to understand these 

markings to safely navigate the ICW. Some examples: 

7

3

1 1

8

4

2 2 3

2

There are three types of symbols:

When following the ICW from New Jersey through Texas, keep yellow triangles on 

your starboard and yellow squares on your port, regardless of the color of the Aid on 

which they appear.

The yellow horizontal band reflector can be found 

on any non-lateral Aid. It simply identifies the Aid as 

marking the ICW.

ICW beacons and buoys do not correspond to IALA-B’s color system because ICW and 

non-ICW routes may travel next to each other in opposing directions – and share the 

same Aids. Thus, when following the ICW, navigate by the yellow symbols; otherwise, 

navigate by the color of the Aid itself. 

Arrows do not indicate 

the actual location of 

the ICW. Arrows depict 

how aids to navigation 

are oriented when 

operating in the ICW.
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

27 28 U.S. Aids to Navigation System

Clearance Gauges

If it is not obvious whether or not there is enough vertical room to travel under a certain 

bridge, boaters should refer to its clearance gauge (affixed to the bridge’s right side 

upon approach). This marks the distance between the “low steel” of the bridge channel 

span and the waterline, not the depth of the water under the bridge.

WATERLINE

LOW STEEL

CLEARANCE (feet) CLEARANCE 

GAUGE

Drawbridge-Opening Protocol

When passage under an open drawbridge is required, the boater 

must make a request of the drawbridge operator. The bridge 

tender will acknowledge the signal. The most common protocols are:

VHF-FM

•	 Boaters may hail the drawbridge operator on channels 13 or 16. 

(Channel 9 should be used in Florida, Georgia, and South Carolina.) 

•	 Always use the low-power output (1 watt) setting.

Sound Signals

Approaching a Closed Draw

•	 An opening signal consists of one prolonged blast (4 to 6 seconds) and one short

blast (1 second); this can be from a whistle, horn, megaphone, or hailer.

•	 The operator will reply with the prolonged-then-short blast if the draw will be

opened immediately. 

•	 Five short blasts in rapid succession mean that the operator cannot comply at that

moment.

Approaching an Open Draw

•	 If the draw is already open, an opening signal (prolonged blast plus short blast)

must be made.

•	 If no reply is received within 30 seconds, you may proceed with caution.

•	 Five short blasts in rapid succession mean that the operator must close the draw;

do not proceed.

Upstream

Bridges

Lighting Systems

Bridges are lit to help boaters navigate under them from sunset to sunrise and during 

other periods of reduced visibility. In general, red lights indicate portions of the bridge 

where it is unsafe to attempt passage, and green lights indicate areas of safe passage. 

See key below.

A

A A

A

E

A

B

E

G

G

E

(Main Channel) D

Fixed Bridge

Double Leaf (Lift) Bascule Bridge Vertical Leaf Span Bridge 

(open)

Double Opening Swing Bridge 

(open)

Vertical Lift Span Bridge

(closed)

closed

open

closed

open

Double-Opening Swing Bridge 

(closed)

A

A A A

A

E

A A A

F F

F

A

A – Piers and supports.

B – Centerline of navigable channel.

C –Three white lights stacked vertically show the preferred route, if 

there is more than one navigable channel.

D – Used on some lift bridges to indicate the lift is closed.

E –Lift is open to vessel traffic.

F – Double-opening swing bridges show three red lights when closed.

G – Double-opening swing bridges show two green lights when open.

6. Special Situations
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

29 30 U.S. Aids to Navigation System

•	 Wait for the lock operator to signal you with horn blasts; additional signals may

include traffic lights or flashing lights.

•	 Enter the lock at reduced speed.

•	 Make sure all passengers remain seated and wear their life jackets.

•	 Tie your craft to the mooring devices after entering; a minimum of 50 feet of

line is recommended. 

•	 Use fenders to avoid damage to your vessel and to lock walls.

•	 When through, wait for the lock operator’s signal (horn and/or lights), then leave

the lock at idle speed.

There is a specific order of lockage priority among vessels. Military and most commercial 

vessels have priority over recreational vessels.

Low-Head Dams

Low-head dams have been built to 

raise the level of rivers or streams for 

various reasons. They can be extremely 

dangerous to small boats and swimmers; so much so, they have been 

nicknamed “drowning machines.”

Small boats may easily become caught 

within the circular motion (hydraulic) of 

the dam’s fast-moving water. The boat 

and its passengers may be unable to escape. Low-head dams are particularly difficult 

to spot on the upstream side; and from any vantage point, they can look harmless. 

Remember that no matter how short a drop the dam may have, it can still be deadly. 

•	 Always portage around low-head dams, regardless of direction of approach. 

Exit the water well before the dam and return well after.

•	 Not all low-head dams are marked by signage or a danger buoy. Therefore,

familiarize yourself with any stream or river before traveling on it. 

•	 When traveling downstream, watch for a smooth horizon line. This is a subtle but

telltale sign that you are approaching a low-head dam. The scenery beyond it 

might have the illusion of being cut off or shortened. 

Controlled-Access Areas

In order to ensure public safety and national security, the Coast Guard periodically establishes controlled-access areas that have special operational or navigational requirements. 

Safety Zones, Security Zones, and Regulated Navigation Areas might require reduced 

speed within a certain radius of a salvage operation, for example, or restrict access 

altogether near a high-profile event or a power plant. These areas should be avoided or 

approached with caution. 

To make sure you know where the controlled-access areas are – and the specific parameters of each – always have the most current nautical chart and the latest Notices 

to Mariners before you head out (www.navcen.uscg.gov). Contact the local Coast Guard 

office or other law enforcement agency for specific details about such areas.

As a general rule, however, it is wise to avoid dams, power plants, and commercial port operation areas, especially those that involve the military, cruise lines, or petroleum facilities. 

Naval Vessel Protection Zones

A Naval Vessel Protection Zone is a permanent controlled-access area that 

surrounds every U.S. naval vessel. The 

parameters are clear: do not come 

closer than 100 yards of a vessel, 

and operate at minimum speed 

within 500 yards of the vessel. Violating a Naval Vessel Protection Zone 

is a felony offense with the possibility of a 

prison sentence and/or fines of up to $250,000. 

Locks

A lock is an engineered structure that enables vessels to move between waterways of 

differing heights. As when traveling under drawbridges, there are specific procedures in 

place for navigating through locks. Specifics may vary in certain regions, but in general:

•	 Stay between the red and green buoys that mark the river’s navigable channel.

•	 Request an opening with a sound signal consisting of one prolonged blast (4 to 6

seconds) and one short blast (1 second) within one mile of the lock; this can be 

made by using the lock’s pull-cord or your whistle, horn, megaphone, or hailer.

Backwash

Boil

Escape Route

Low-head Dam

OPERATE AT MINIMUM SPEED

KKEEP O EEP OUUTT

100 YARDS

500 YARDS

 If you feel you must enter a controlled-access area to ensure safe navigation, 

immediately contact the Coast Guard on VHF-FM Channel 16.
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

31 32 U.S. Aids to Navigation System

7. Always Wear Your Life Jacket!

(and require the same of your passengers)

The number one cause of on-the-water fatalities is drowning. The number one way to 

prevent drowning is to wear a life jacket.

The U.S. Coast Guard requires recreational vessels to have a wearable life jacket for 

each person on board. 

All life jackets must be:

•	 U. S. Coast Guard-approved.

•	 The proper size for the intended wearer.

•	 In good and serviceable condition.

•	 Properly stowed (readily accessible).

Children Must Wear Life Jackets 

Federal regulations require that on a 

recreational vessel underway, children 

under 13 must wear an appropriate 

U. S. Coast Guard-approved life jacket, 

unless they are below decks or in 

an enclosed cabin. Within a state’s 

waters, if that state has established a 

child lifejacket wear requirement, that 

state’s requirement applies. 

The Coast Guard recommends all passengers wear a life jacket at all times when the 

vessel is underway.

Tips for a Proper Fit – Try It On

•	 Use the manufacturer’s label as a guide to choosing the proper life jacket for your

size and weight. It should have a comfortably snug fit.

•	 With all straps, zippers, and ties securely fastened, raise your arms over your head. 

The jacket should stay in place and not ride up.

•	 With your arms at your sides, have someone lift your life jacket straight up at the

shoulders. If the jacket comes up more than a few inches, it is too loose. 

•	 It is best to try on a life jacket before a boat trip.

•	 Life jackets designed for adults will not work for children!

America’s Waterway Watch

The U.S. Coast Guard is asking boaters to help keep America’s waterways safe and 

secure.

The Coast Guard has developed a program called America’s Waterway Watch 

(www.americaswaterwaywatch.org). It asks boaters to call 877-24WATCH if they notice 

suspicious activity or behavior on or near the water.

Things to report include:

•	 Someone taking pictures, video, or

making sketches of facilities like 

bridges, tunnels, ferry transport 

systems, fuel docks, or power plants.

•	 Someone asking a series of questions about access to one of these 

facilities.

•	 Someone anchoring, fishing, or

diving in an area not typically used 

for that activity.

•	 Unattended vessels in unusual

locations.

•	 Unusual transfer of personnel

or cargo while underway.

•	 Seeing a hole in a security fence around an industrial facility.

Do not take matters into your own hands. Call 877-24WATCH. In cases of immediate 

danger to life or property, call the Coast Guard on Channel 16 VHF-FM, or dial 911 for 

emergencies.
U.S. Aids to Navigation System www.uscgboating.org www.uscgboating.org

33 34 U.S. Aids to Navigation System

Key to the U.S. Aids to Navigation System (IALA-B) 

How to Report Aids to Navigation Discrepancies to the Coast Guard

Please report discrepancies or outages to any Aid to Navigation (GPS, DGPS, buoys, 

lights, dayboards, etc.) to the nearest U.S. Coast Guard station. You can do this 24 

hours a day, 7 days a week via radio, telephone, fax, visiting www.navcen.uscg.gov, or by 

e-mailing navcen@uscg.mil. To reach the U.S. Coast Guard Navigation Center by 

telephone, call (703) 313-5900. 

Reporting can help prevent accidents caused by such defects; you will be helping other 

boaters stay safe.

All Aids to Navigation are Protected By Law 

It is 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.

B – Black

Bn – Beacon 

examples:

C – Can Buoy

examples:

 

F – Fixed 

Fl – Flashing 

Fl (2) – Group Flashing 

 

Fl (2+1) – Composite Group-Flashing

G – Green

Iso – Isophase 

J – Junction (S or T Dayboard)

examples:

M – Safe Water (Octagonal)

example:

Mo (A) – Morse Code letter “A” 

 

N – Nun Buoy 

examples:

Oc – Occulting 

Or – Orange 

Pri – Private

Q – Quick (Flashing) 

R – Red

S – Square Dayboard

examples:

s – seconds

T – Triangle Dayboard

examples:

W – White

 Y – Yellow

Surprisingly Comfortable

Today’s life jackets are lightweight, easy to move in, and come in many sizes, styles, 

and shapes for every person and every sport. (There are even ones for pets!) Some

examples:

Inflatable

for general recreational 

boating

Belt Pack Inflatable

for general recreational 

boating

Vest-Type Flotation Aid

for personal watercraft, 

waterskiing, and water 

sports

Child Hybrid Inflatable

for general recreational 

boating

Child Life Jacket

for general recreational 

boating

Flotation Aid

for general recreational 

boating

Vest Type

for general 

recreational boating

Inflatable Fishing Vest

for angling and 

hunting

Paddling Jacket

for paddlesports

Offshore Vest

for offshore boating 

and racing

Position of light
U.S. Aids to Navigation System www.uscgboating.org

35

Most boating accidents are preventable! Be sure to:

•	 Always wear your life jacket and

require the same of your passengers

•	 Never boat under the influence

•	 Take a boating safety course

•	 Get a free Vessel Safety Check

www.uscgboating.org

06/2011

For more information please contact: