Washington State Department of Natural Resources, Nearshore Habitat ProgramThese data are part of a long-term monitoring effort to survey floating kelp canopies annually. The dataset contains the following components: 1) layers indicating floating kelp persistence combined (persistence_all_kelp) and split by species (perstistence_bull_kelp, persistence_giant_kelp, persistence_mixed_kelp) , 2) A combined inventory from the 5 most recent years (kelp_recent_5yr), 3) A spatial index (map_index_points and map_index_polygons), 4) A summary table describing kelp characteristics for each year that link to the spatial index (summary_kelp_stats). Data are derived from photo interpretation of low tide aerial photography collected in the late summer, the season of maximum bed extent. Polygons represent bed extent, or planimeter, which include the kelp canopy floating on the surface and small gaps between plants (25-meter threshold for delineating discrete beds). Users who wish to use the most precise inventory estimates and compare area over multiple years should use the tabular summary tables which summarize area by map_index. The tabular estimates are more precise because they are based on the source imagery. The area estimates in the feature classes reflect subsequent processing. Methods of subsequent processing have varied with changes in technology since 1989, resulting in noticeable differences among years in the spatial data that preclude detailed comparison of spatial data across years. Major methodological changes include: 1) a format change from vector (CAD) in 1989 to raster (20 m cell size) in 1994; 2) In 2010, the resolution changed from 20 meter to 4 meter resolution.ArcGIS FeatureLayerhttps://hub.arcgis.com/datasets/fccecc7691da4425aa7a37e1bd07be72_9engState of Washington Geospatial Open Data PortalPublicMap Index Polygons [Washington (State)]Web servicesWashington (State)Last Modified: 2026-02-10