The San Francisco Bay-Delta estuary contains the greatest expanse of coastal wetlands on the West Coast south of Alaska, providing critical feeding and breeding habitat for hundreds of species of animals. Wetlands help improve water quality by trapping chemicals from polluted runoff before they get into rivers and oceans; they also decrease risks associated with flooding and prevent erosion. And they're critical to sustaining the aquatic food chain throughout the Bay-Delta system.
The Bay Area's wetlands include many different types of habitat, each supporting different vegetation and wildlife. Tidal marshes are open to the bay's tides; they vary from salt marsh in the bay to brackish marsh in the delta. Seasonal wetlands are filled by winter rains and often are dry by mid-summer. Riparian wetlands are freshwater, streamside wetlands.
The loss of these wetlands has pushed many species, including the California clapper rail and the salt marsh harvest mouse, to the brink of extinction.
Years of Destruction
Over the past 150 years, the Bay-Delta estuary has been transformed beyond recognition; it is now the most altered major estuary in the world. Overall, the size of the bay has been reduced by more than a third since 1850. Of all the habitat types in the Bay-Delta, wetlands have been most severely damaged. The destruction of wetlands is one of the major causes of the overall decline of the estuary's health.
More than half a million acres of tidal marsh have been destroyed or converted, and an astounding 97 percent of the delta's historic tidal marshes have been diked or filled. Eighty-two percent of the bay's tidal wetlands have disappeared. Other wetland types -- riparian, seasonal, brackish, and freshwater -- have also suffered drastic losses. While the restoration and enhancement of 21,793 acres, or roughly 34 square miles, is important, it represents less than 4 percent of the Bay Area's original wetlands. In addition, because some species depend on a single habitat type, the overall amount of all wetlands is just one measure of their health in the Bay Area.
Progress Made, Much to Do
During the 1960s, the loss of tidal wetlands slowed dramatically, with the creation of the Bay Conservation and Development Commission, which regulates bay filling. The loss of seasonal wetlands began to slow in the late 1980s, when awareness of the problem and activism to correct it increased. The growing wetlands-restoration movement, involving dozens of groups and agencies, has made significant progress in recent years, but much remains to be done. Tens of thousands of acres of salt ponds, agricultural land, and degraded wetlands around the bay and delta have yet to be restored -- even as development continues to threaten these critical areas. Additional efforts will be needed to prevent more development of wetlands, which could threaten both the gains already made and potential restoration opportunities.