U.S. Aids to Navigation System (ATON)

Buoys and markers are the "traffic signals" that guide vessel operators safely along some waterways. They also identify dangerous or controlled areas and give directions and information. As a recreational boat or PWC operator, you will need to know the lateral navigation markers and non-lateral markers of the U.S. Aids to Navigation System.

Lateral Markers

These navigation aids mark the edges of safe water areas; for example, directing travel within a channel. The markers use a combination of colors and numbers, which may appear on either buoys or permanently placed markers.

Illustrations of Markers:

What the Markers Mean:

Red colors, red lights, and even numbers indicate the right side of the channel as a boater enters from the open sea or heads upstream.

Green colors, green lights, and odd numbers indicate the left side of the channel as a boater enters from the open sea or heads upstream.

Buoy with green stripe on top, red below, and light on top

Red and green colors and/or lights indicate the preferred (primary) channel. If green is on top, the preferred channel is to the right as a boater enters from the open sea or heads upstream; if red is on top, the preferred channel is to the left.

Buoy with red stripe on top, green below, and light on top

Lighted Buoys use the lateral marker colors and numbers discussed above; in addition, they have a matching colored light.

Nuns are red cone-shaped buoys marked with even numbers.

Cans are green cylindrical-shaped buoys marked with odd numbers.

Daymarks are permanently placed signs attached to structures, such as posts, in the water. Common daymarks are red triangles (equivalent to nuns) and green squares (equivalent to cans). They may be lighted also.

Intracoastal Waterway System

The Intracoastal Waterway (ICW) is chain of channels that provide an inland passage along the U.S. coast. Buoys and markers used in this system are identified by yellow symbols and serve a dual purpose—they are navigational aids for the lateral system and are markers for the ICW.

If you are following the ICW from New Jersey to Brownsville, Texas, in a clockwise direction:

Any marker displaying a yellow triangle should be passed by keeping it on the starboard (right) side of your vessel.
Any marker displaying a yellow square should be passed by keeping it on the port (left) side of your vessel.

Red triangle daymark displaying a yellow triangle

Green square daymark displaying a yellow square

Boating Basics: On the Water