Boating Basics: On the Water

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.

Buoy and Marker Color and Number Descriptions	Illustrations
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.
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.
Nuns are cone-shaped buoys marked with red colors and even numbers.
Cans are cylindrical-shaped buoys marked with green colors and odd numbers.
Lighted Buoys use the lateral marker colors and numbers discussed above; in addition, they have a matching colored light.
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.