Sargassum muticum is an introduced alga that is widely distributed in Washinton State saltwater areas. This dataset summarizes Sargassum occurrence using data from the ShoreZone Inventory. Sargassum is classified as being patchy (less than 50%) or continuous (greater than 50%) along each unit of shoreline (an area with similar physical characteristics). The majority of the shoreline is described by line data, polygon features exist in some areas with extensive shallows. The ShoreZone Inventory includes all saltwater shorelines statewide. It was completed between 1994 and 2000 using aerial videography collected at low tide. For more information on the inventory, see http://www.dnr.wa.gov/programs-and-services/aquatics/aquatic-science/nearshore-habitat-inventory