Estuaries are the interface of rivers, ocean, atmosphere, and dense human settlement. Their variability is driven by a large array of natural and anthropogenic forces. This website describes the long-term research and observation project in the San Francisco Bay-Delta that serves to measure and understand changes in water quality due to these forces. It measures the basic elements of water quality that define the sustainability of the Bay as habitat for fish and organisms of the lower trophic levels. Using both oceanographic sensors and discrete water collection, we measure salinity, temperature, light extinction coefficient, chlorophyll-a, dissolved oxygen, suspended particulate matter, nitrate, nitrite, ammonium, silicate, and phosphate.