Forty percent of the state drains through the delta at the confluence of the Sacramento and San Joaquin rivers, which then meet the salty water of the Pacific Ocean in the bay. This mixture is carried through the Golden Gate with each tide. The San Francisco Bay and estuary contain 90 percent of California's remaining coastal wetlands and are important stops for millions of migrating waterfowl. The current wetland acreage in California is estimated to be 450,000. Estimates of the historic acreage is as high as 4 million in California alone.
Wetlands are the base of many food webs, supporting a great diversity of wildlife.
Not only is it vital to the survival of millions of over-wintering waterfowl, but it is the primary nursery for many animals, including the state's largest run of Chinook salmon and its only run of striped bass. Almost the entire California population of northern shovelers winters in the bay, as do two-thirds of the state's canvasbacks and greater and lesser scaups. Wetlands are described as an area saturated or covered by water at least part of the year. Marine and estuarine wetlands are connected to the ocean and include coastal wetlands, such as tidal marshes. Lacustrine wetlands are found around lakes, while riverine wetlands are associated with rivers and streams.