- Lake Whatcom (from the Lummi word for “loud water”) is located in Whatcom County, Washington, United States. It is the drinking water source for approximately 85,000 residents in the city of Bellingham as well as Whatcom County. It is approximately 10 miles (16 km) in length and 1 mile (1.6 km) in width at its widest. Lake Whatcom is located and managed within three political jurisdictions: the city of Bellingham, Whatcom County, and the Lake Whatcom Water and Sewer District. The lake is a popular area for motor boating, swimming, fishing, and other recreational activities.