The U.S. Geological Survey (USGS) monitors water quality and suspended-sediment transport in the San Francisco Bay (Bay) as part of a multi-agency effort to address estuary management, water supply, and ecological concerns. The San Francisco Bay area is home to millions of people, and the Bay teems with plants and both resident and migratory wildlife, and fish. Freshwater mixes with salt water in the Bay and is subject to riverine influences (floods, droughts, managed reservoir releases, and freshwater diversions) and marine influences (tides, waves, and effects of salt water). To understand this environment, the USGS along with its cooperators (see “Acknowledgments”), has been monitoring the Bay’s waters continuously since 1988.