Lake Whatcom is a large, deep, monomictic lake in the Puget lowlands of Washington State. Expanding development from the city of Bellingham and a large diversion of water from the Nooksack River to the lake are two recent impacts. Bellingham depends on the lake as its sole drinking and industrial water supply. Additionally, the lake is an important recreational resource. Monitoring of the lake began in 1962 and was continuous to 1972, and recent work began in 1979. These data and information from sediment cores have been used to determine trends in water quality. Historically, watershed uses were mainly logging and some coal mining. Sedimentation rates based on Pb-210 were about 0.5 cm/yr. More recently, sedimentation rates have increased to 0.8–1.2 cm/yr., apparently due to increased runoff related to urbanization and the diversion of Nooksack River water containing glacial meltwater with high particulate loads. Much of the particulate material is sedimented in a 6.5 ha lake below the diversion tunnel (volume has decreased 20 percent since 1962), but very fine particulates are transported through this lake to Lake Whatcom. These silt and clay-sized particles may sorb phosphorus descending through the water column. Nutrient concentrations and sediment metal concentrations increase toward the urbanized portions of the watershed. The city water intake is located in the shallowest, most nutrient-rich basin, containing the greatest development densities. Water level regulation is also an issue due to conflicting uses of shoreline development, water storage and use and downstream encroachment. Due to the flashiness of watershed streams, water and sediment transport can cause problems for lake level manipulation and water quality. A Phase 1 lake restoration study funded by the State of Washington is underway, and results will be discussed.