The Shrinking Bay

The San Francisco 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 remains.

Once a 400,000 acre tidal marsh with extensive uplands at the confluence of the Sacramento and San Joaquin rivers, the Delta was diked and channelized in the late 1800s and early 1900s for conversion 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.

Historical Aquatic Ecosystem
(About 150 years ago)

This map shows the historical distribution of tidal wetland, tidal mudflat, and shallow and deep open water circa 1770-1820. Tidal wetland represented about 37% of the total aquatic habitat in the historical bay ecosystem. Tidal mudflat represented about 10% of the total aquatic area, and the remaining 53% was occupied by open bay water and tidal channels.


Current Aquatic Ecosystem

This map shows the current (circa 1997) extent of tidal wetland, tidal mudflat, and shallow and deep ocean water. The former extent of these habitats that has been converted to others uses is shown in white. There has been an 82% reduction in tidal wetland acreage, a 42% reduction in tidal mudflat acreage, and a 7% percent reduction in open water area. All together, nearly 40% of the historical Bay's aquatic ecosystem has been lost.