Birch Bay (Tsan-wuch, Say-wak) is a census-designated place (CDP) along the shore of the bay named Birch Bay in Whatcom County, Washington, United States. The population was 8,413 at the 2010 census, a 69.6% increase over the 4,961 individuals in the 2000 census. As of the 2020 census, the population was 10,115.