The San Francisco Bay-Delta Estuary
Each of the Central Valley’s rivers and streams is incredible in its own way, but together they combine to form one of California’s – and Earth’s – most unique ecosystems: the San Francisco Bay-Delta estuary. The estuary and its watershed cover nearly 40% of California’s land area, encompassing the Sacramento and San Joaquin Rivers, the many tributary streams of the Sierra Nevada, Cascade and Coast Ranges that flow into them, the inland Delta where these rivers converge, San Francisco Bay itself, and the nearshore coastal waters of the Gulf of the Farallones. The Bay-Delta is the largest estuary on the entire west coast of North and South America and includes the largest inland delta and largest wetland complex.
What Makes the Estuary Special
When freshwater flow from Central Valley rivers reaches the Bay-Delta it mixes with salty water to create an estuary, a brackish water (part salty, part fresh) ecosystem that is a highly productive nursery for fish, birds, marine mammals, and invertebrates like crabs and shrimp. Freshwater inflow stimulates the food web in the estuary. It increases production of planktonic animals which are at the bottom of the food chain. High flows carry sediments to form floodplains, wetlands, and beaches. Estuarine habitat supports hundreds of plants and animal species, many found nowhere else on earth, and commercially valuable fisheries for salmon, starry flounder, sturgeon, and splittail.
The Sacramento-San Joaquin Delta: From Marsh to Agriculture
The Sacramento-San Joaquin Delta originally consisted of a 400,000-acre tidal marsh and hundreds of thousands of acres of other habitats at the confluence of the Sacramento and San Joaquin rivers. In the late 1800s and early 1900s, a massive effort to add levees to major waterways and fill minor ones with soil resulted in the conversion of the Delta into agricultural islands. Today only two percent of the original marsh habitat remains, and many of the islands have subsided (sunk) to below sea level behind their protective levees.
San Francisco Bay: Shrinking Habitat
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 due to shoreline development and reduced sediment inflows, 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.
The Impact of Dams and Water Diversions
On average, about half of the water from the estuary’s watershed is captured upstream of the Delta by thousands of dams and diversions, or exported by giant pumps from the Delta to corporate agribusiness in the San Joaquin Valley, and to cities in the Bay Area and Southern California. This massive water mining reduces the freshwater flows that sustain the estuary. As a result, harmful algal blooms and other water quality problems have increased. Reduced flows also degrade the quality and quantity of wildlife habitat by reducing nutrient and sediment inflows and eroding beaches and wetlands.
Lower freshwater flows further disrupt the spawning, rearing, and migration of many aquatic species. Populations of numerous estuary-dependent fish have fallen to record or near-record lows, including the delta smelt—once the most common fish species in the estuary. These impacts have also contributed to the closure of California’s commercial salmon fishery for recent years, leading to continued job losses in fishing and seafood-related industries.
Friends of the River: Restoring the Bay-Delta Estuary
Friends of the River is committed to restoring the health of both the Bay-Delta estuary and the many rivers that feed it. We work to:
- Secure new regulatory requirements to significantly increase the amount of fresh water that flows from Central Valley rivers into and through the Delta and San Francisco Bay—and to defeat “Voluntary Agreements” that would gut these protections
- Revive dry rivers in the watershed and reconnect them to the Bay-Delta
- Defeat proposals to build more dams and diversions which would further cut the freshwater flow in the estuary