At a Glance
The San Francisco Bay-Delta Estuary is the largest estuarine system on the west coasts of both North and South America. A rich national treasure containing more than 90 percent of the state's remaining coastal wetlands, the Estuary ranges from the salty waters of San Francisco Bay to the brackish waters of the Sacramento-San Joaquin Delta. The Estuary’s vast upstream watershed drains more than 40 percent of California’s land mass, including the freshwater streams of the Sierra Nevada and Coast Ranges.
Most of the fresh water that creates the estuary flows from the rugged western slopes of the Sierra Nevada and Cascade mountain ranges. From south to north, winter rains average from 40 to 80 inches a year, feeding the streams carrying runoff and snowmelt to the great Central Valley below. Unfortunately, on average only about 60 percent of this freshwater flow reaches San Francisco Bay: the rest is captured upstream of the Delta by thousands of dams and diversions or exported from the Delta to San Joaquin agribusiness and Southern California cities by the giant pumps of the federal and state water projects. This massive water mining of the estuary severely degrades water quality and habitat conditions and interferes with spawning, rearing, and migration of many aquatic species.
The Delta was once a 400,000 acre tidal marsh with extensive uplands at the confluence of the Sacramento and San Joaquin rivers. Beginning in the late 1800s and early 1900s, it was diked and channelized, and converted into agricultural islands. Today only two percent of the original marsh habitat remains, and many of the islands have subsided to below sea level behind their protective levees.
San Francisco Bay covers 400 square miles and has an average depth of 14 feet with depths plunging to 360 feet at the Golden Gate. The Bay has shrunk by a third in the last 150 years, and only about 25 percent of its original wetland, riparian, and tidal mudflat habitat still exists. Even so, the bay supports commercial bait shrimp, herring, and Dungeness crab fisheries — the only urban commercial fisheries in the nation.
At the same time, San Francisco Bay is also the largest harbor on the U.S. Pacific Coast, with more than 67,000,000 tons of cargo passing annually through the Golden Gate. Much of this cargo is crude oil, and spills and other industrial accidents remain a constant threat to estuarine fish and wildlife.