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Boating Basics

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.

Red buoy with light and number

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 buoy with light and number

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.

A lateral marker with red and green colors

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 red cone-shaped buoys marked with even numbers.

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

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

Red cone shaped "nun" buoy
A nun
Green cylindrical-shaped "can" buoy
A can
Buoy with red stripe on top, green below, and light on top
A lighted buoy

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.

Green and red daymark

Red Right Returning is a reminder of the correct course when returning from open waters or heading upstream.

Boat entering channel: red buoy on starboard, green on port

Non-Lateral Markers

Non-lateral markers are navigational aids that give information other than the edges of safe water areas. The most common are regulatory markers which are white and use orange markings and black lettering. These markers are found on lakes and rivers.


Squares indicate where to find food, supplies, repairs, etc. and give directions and other information.


Circles indicate a controlled area such as speed limit, no fishing or anchoring, ski only or no skiing, or "slow, no wake."


Crossed diamonds indicate areas off limits to all vessels such as swimming areas, dams, and spillways.


Diamonds warn of dangers such as rocks, shoals, construction, dams, or stumps. Always proceed with caution.

Information marker: White buoy with directions inside an orange square
Controlled area marker: White buoy with speed limit inside an orange circle
Exclusion marker: White buoy with orange crossed diamond and labeled Boats Keep Out
Danger marker: White buoy with an orange diamond that warns of danger

Other Non-Lateral Markers

Safe Water Markers are white with red vertical stripes and mark mid-channels or fairways. They may be passed on either side.

Inland Waters Obstruction Markers are white with black vertical stripes and indicate an obstruction to navigation. You should not pass between these buoys and the nearest shore.

Mooring Buoys are white with a blue horizontal band and are found in marinas and other areas where vessels are allowed to anchor.

Safe Water Markers: Red and white vertically striped buoys
Safe water marker
Inland waters Obstruction Markers: Buoy with black and white vertical stripes
Inland waters obstruction marker
Mooring buoy
Mooring buoy