<P> By the end of the 19th century, these "slickens" had filled in much of the shallow bay flats, raising the entire bay profile . New marshes were created in some areas . </P> <P> In the decades surrounding 1900, at the behest of local political officials and following Congressional orders, the US Army Corps began dredging the Sacramento and San Joaquin Rivers and the deep channels of San Francisco Bay . This work has continued without interruption ever since an enormous federal subsidy to San Francisco Bay shipping . Some of the dredge spoils were initially dumped in the bay shallows (including helping to create Treasure Island on the former shoals to the north of Yerba Buena Island) and used to raise an island in the Sacramento - San Joaquin Delta . The net effect of dredging has been to maintain a narrow deep channel--deeper perhaps than the original bay channel--through a much shallower bay . At the same time, most of the marsh areas have been filled or blocked off from the bay by dikes . </P> <P> Large ships transiting the bay must follow deep underwater channels that are maintained by frequent dredging as the average depth of the bay is only as deep as a swimming pool--approximately 12 to 15 ft (4--5 m). Between Hayward and San Mateo to San Jose it is 12 to 36 in (30--90 cm). The deepest part of the bay is under and out of the Golden Gate Bridge, at 372 ft (113 m). </P> <P> In the late 1990s, a 12 - year harbor - deepening project for the Port of Oakland began; it was largely completed by September 2009 . Previously, the bay waters and harbor facilities only allowed for ships with a draft of 46 ft (14 m), but dredging activities undertaken by the United States Army Corps of Engineers in partnership with the Port of Oakland succeeded in providing access for vessels with a 50 - foot (15 m) draft . Four dredging companies were employed in the US $432 million project, with $244 million paid for with federal funds and $188 million supplied by the Port of Oakland . Some 6,000,000 cubic yards (4,600,000 m) of mud from the dredging was deposited at the western edge of Middle Harbor Shoreline Park to become a 188 - acre (76 ha) shallow - water wetlands habitat for marine and shore life . Further dredging followed in 2011, to maintain the navigation channel . This dredging enabled the arrival of the largest container ship ever to enter the San Francisco Bay, the MSC Fabiola . Bay pilots trained for the visit on a simulator at the California Maritime Academy for over a year . The ship arrived drawing less than its full draft of 50 feet 10 inches (15.5 m) because it held only three - quarters of a load after its stop in Long Beach . </P>

What is the average depth of san francisco bay