(a) Lateral marks define the port and starboard sides of a route to be followed. They may be either beacons or buoys.

(b) Sidemarks are lateral marks which advise the mariner to stay to one side of the mark. Their most frequent use is to mark the sides of channels; however, they may be used individually to mark obstructions outside of clearly defined channels. Sidemarks are not always placed directly on a channel edge and may be positioned outside the channel as indicated on charts and nautical publications.

(c) Preferred channel marks indicate channel junctions or bifurcations and may also mark wrecks or obstructions which the mariner, after consulting a chart to ascertain the location of the obstruction relative to the aid, may pass on either side. Preferred channel marks have red and green horizontal bands with the color of the topmost band indicating the preferred channel. If the topmost band is green, the mark serves as a port hand mark for vessels following the preferred channel proceeding in the Conventional Direction of Buoyage, and as a starboard hand mark for the other channel. Beacons would have square daymarks, while buoys would be can or pillar buoys. If the topmost band is red, the mark serves as a starboard hand mark for vessels following the preferred channel proceeding in the Conventional Direction of Buoyage, and a port hand mark for the other channel. Beacons would have triangular daymarks, while buoys would be nun or pillar buoys.

(d) The above color schemes apply to IALA Region B. Marks located in the IALA Region A exhibit reversed color significance: port hand marks will be red when following the Conventional Direction of Buoyage, and starboard hand marks will be green. The meaning of daymark and buoy shapes is identical in both regions.

(e) Certain marks on the Intracoastal Waterway may exhibit reversed lateral significance. See § 62.49.