The San Francisco Bay Estuary
The broad blue-green water body in the center of it all—San Francisco Bay—provides Bay Area residents with their inimitable sense of place and iconic geography. Underneath the water and at its surface, in its wetlands and watersheds, the Bay is also habitat for hundreds of species of fish and wildlife, including several endangered species and the multitudes of birds that reside here or migrate along the Pacific Flyway of North America. It is San Francisco Bay that defines a world-renowned tourist destination and supports a thriving state and local economy, enabling our region to be a global center of water-borne commerce and providing an enviable quality of life for over 7.5 million residents. Caption: Coyote Hills from shoreline trail. Don Edwards San Francisco Bay National Wildlife Refuge. Photo by Ryan Koenigs
The Estuary’s watershed, the largest in western North America, covers 60,000 square miles and drains 40 percent of California. This is the largest estuary in western North America and a biological resource of tremendous importance—a productive nursery for juvenile fish and crabs and a year-round home for countless plant and animal species. Two-thirds of the State’s salmon pass through the Bay, a commercial fishery continues for Pacific herring, and nearly half of Pacific coast waterfowl and shorebirds depend upon the Bay’s mudflats for sustenance during their migrations.
Roughly half of California’s surface water supply falls as rain or snow into our watershed. Half of that is diverted for use by farms, factories or households. We divert freshwater from its watershed to serve 18 million people and over 4 million acres of agricultural land. At the same time, we count on “our watershed” to absorb over half a billion gallons of treated wastewater each day, along with vast quantities of urban stormwater and floodwaters during rainstorms. The Bay delivers these services while still providing habitat for fish, birds, and other wildlife, recreational opportunities for people, and supporting our maritime industries.
Upstream from the Bay, the San Joaquin-Sacramento River Delta is a thousand-square-mile triangle of diked and drained wetlands. Only small remnants of once-extensive tule marshes still fringe the sloughs and channels that wind between flat, levee-rimmed farmlands on the Delta islands. Before it was diked and drained, the Delta gathered in the fresh waters of the Sacramento, San Joaquin, Mokelumne, and Cosumnes rivers, and moved them all downstream, through a complex array of tidally influenced channels, into salty San Francisco Bay. Today, the Delta is the engineered junction of one of the world’s largest plumbing systems, where fresh water is diverted to supply California’s population centers and Central Valley agriculture.
San Francisco Bay includes four smaller bays. Suisun Bay and the diked wetlands of Suisun Marsh are the least salty of these, just downstream of the Delta. Saltier San Pablo Bay is west of Carquinez Strait. The saltiest basins are the Central Bay, which connects with the ocean through the Golden Gate, and the South Bay, a large, shallow lobe extending off the Central Bay, south of the Dumbarton Narrows.
Bay HealthThe Bay is less polluted than in past decades, thanks to our investments in sewage treatment, improved solid waste handling, and regulation of chemicals like DDT and PCBs.
The Bay today is safe for recreation and deeply valued by Bay Area residents and visitors from around the world. However, remaining pollution problems will be challenging to clean up. Some problems, such as those caused by mercury, a legacy from the Gold Rush era, will take decades to resolve. Mercury and other pollutants accumulate in fish and wildlife, so we must limit the amount of Bay fish we eat. These pollutants also threaten birds and other animals at the top of the food web.
Many of the remaining sources of pollution are widespread, hard to control, and diffuse, such as the runoff from streets, driveways, and other urban surfaces and we continue to release new chemicals into the Bay that do not break down easily, without analyzing their ecological risks. Concentrations of these chemicals— such as certain flame retardants—are rising in the Bay, suggesting that our grandchildren may confront new pollution legacies.
Filling the Bay with sediment has essentially ended, and thousands of acres of wetlands are being restored in one of the largest habitat restoration projects in the nation. We know that animal populations will respond slowly as these restored landscapes mature. Native fishes and birds are already using newly restored marshes, and these productive nursery areas should bolster their populations in the future. Wildlife face additional threats from pollutants that can have subtle toxic effects on their health, and from invasive species and ubiquitous urban-dwelling or introduced predators like crows, feral house cats, and rats. This results in bird populations increasing in some areas, but declining in others. Many fish populations are also declining in the Bay, indicating that some of goals of the Comprehensive Conservation and Management Plan have still not been met. These declines are due, at least in part, to continued low annual freshwater flows into the Bay as water is diverted from its rivers and the Delta. Our water diversion capacities and practices now result in low freshwater inflows to the Bay even when California is not experiencing a drought.
Shrimp and crab populations, representing the important invertebrate part of the food web, have been growing, although the composition of these populations is changing. With less fresh water coming into the Bay, the brackish water habitat of the native San Francisco Bay shrimp is shrinking, and populations of shrimp that live in more ocean-like conditions are growing. Favorable conditions in the nearby ocean are contributing to the recent growth in shrimp and crab populations.
The good news is that our efforts of all our San Francisco Estuary Partnership agencies and organizations to improve the health of the Bay are having an impact. Rather than disposing of much of the sediment we dredge from shipping channels and ports into the Bay, we now use much of this material to create new wetlands, and we’ve reduced the discharge of chemicals such as copper, nickel, and mercury from our municipal and industrial wastewater plants. We have greatly improved access to the Bay through ongoing efforts to complete the Bay Trail, and more citizens than ever before are volunteering their time to clean and restore the Bay’s wetlands and watersheds. See a Summary of Bay Health from the 2011 State of the Bay Report