Birch Bay (WA 50.5) is in the northern Salish Sea, just south of the Strait of Georgia in Blaine, Washington, USA. This site is located within the Washington State Department of Natural Resources Cherry Point Aquatic Reserve. The primary species at this site are native eelgrass, Zostera marina, and non-native eelgrass, Zostera japonica. Between 2012-2024, native seagrass Z. marina decreased, and Z. japonica increased at the Birch Bay SeagrassNet transect. Only transect B (0 m, MLLW) is monitored at this site.