High Quality Content by WIKIPEDIA articles! Lake Whatcom Reservoir (from the Lummi word for "loud water") is located in Whatcom County, Washington. 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 total in length and 1 mile in width at its widest. Lake Whatcom is located and managed within 3 political jurisdictions, the City Of Bellingham, Whatcom County and Lake Whatcom Water and Sewer District. The lake is a popular source of motor boating, swimming, fishing and other recreational activities.