Aids to navigation used in the USWMS are an organized system of buoys with conspicuous shapes, colors, and markings primarily established to assist vessel operators by indicating position or the safe and proper course on which to proceed.

(1) Aids to navigation used in the lateral system indicate to a vessel operator the preferred direction of travel for safe passage principally by defining the port or left-hand side and the starboard or right-hand side of a route to be followed. Buoys used in the cardinal system indicate to a vessel operator the preferred direction of travel for safe passage through distinct colors which have meaning in relation to the cardinal points of the compass, north, east, south, and west.

(2) On a well-defined channel including a river or other relatively narrow natural or improved waterway, an aid to navigation shall normally be a solid colored buoy. A buoy which marks the left side of the channel viewed looking upstream or toward the head of navigation shall be colored all black. A buoy which marks the right side of the channel viewed looking upstream or toward the head of navigation shall be colored all red. On a well defined channel, solid colored buoys shall be established in pairs, one on each side of the navigable channel which they mark, and opposite each other to inform the user that the channel lies between the buoys and that he or she should pass between the buoys.

(3) On an irregularly defined channel, solid colored buoys may be used singly in staggered fashion on alternate sides of the channel provided they are spaced at sufficiently close intervals to inform the user that the channel lies between the buoys and that he or she should pass between the buoys.

(4) Where there is no well-defined channel, or when a body of water is obstructed by objects whose nature or location is such that the obstruction can be approached by a vessel from more than one direction, supplemental aids to navigation having cardinal meaning may be used. The use of aids to navigation having cardinal meaning is discretionary provided that they are not used on waters considered navigable by the United States Coast Guard Commandant unless specifically permitted by the United States Coast Guard.

(5) Aids to navigation conforming to the cardinal system shall consist of three distinctly colored buoys.

(a) A white buoy with a red top may be used to indicate to a vessel operator that he or she must pass to the south or west of the buoy.

(b) A white buoy with a black top may be used to indicate to a vessel operator that he or she must pass to the north or east of the buoy.

(c) In addition, a buoy showing alternate vertical red and white stripes may be used to indicate to a vessel operator that an obstruction to navigation extends from the nearest shore to the buoy and that he or she must not pass between the buoy and the shore. The number of white and red stripes is discretionary, provided that the white stripes are twice the width of the red stripes.