The waters of the United States are marked for safe navigation by the lateral system of buoyage. This system employs a simple arrangement of colors, shapes, numbers and light characteristics to show the side on which a buoy should be passed when proceeding in a given direction. The characteristics are determined by the position of the buoy with respect to the navigable channels as the channels are entered from seaward. Conversely, when proceeding toward the sea or leaving port, red buoys are passed on the port side and green buoys on the starboard side.
Red buoys are always even-numbered.
Green buoys are odd-numbered. Red and white vertically stripped buoys mark the center of the channel. In recent years, modification to certain aids to navigation located on coastal and inland waters have been completed. These changes apply to aids used in both the lateral and state waterway marking systems. Starboard-hand buoys are painted red, with red fixed or flashing lights.