X-Marker, IALA Special

An IALA special mark indicates an area or feature shown on the chart rather than a navigational danger: spoil grounds, military exercise zones, cable and pipeline routes, data-collection buoys, and traffic-separation features. It is yellow, may carry a single yellow X (cross) topmark, and shows a yellow light with any rhythm not used by white lights. It carries no navigational meaning by color alone; the mariner must consult the chart and notices to learn what it marks.