Originally part of a much larger tidal marsh complex that fringed San Pablo Bay, including along the shoreline of West Contra Costa County. The Chelsea wetlands are the remaining 12 acres (4.9 ha) of undeveloped coastal marsh between Hercules and Pinole.[1] The seasonal marsh was diked off and a large portion of it filled sometime in the late 19th/early 20th century during the development of the Pinole/Hercules area. It has been further degraded by the dumping of soil from more recent surrounding construction projects.[1]
Hercules was seeking to restore funds for habitat restoration of lower Pinole Creek in 2012, to protect against flooding into the adjacent city neighborhood, and to restore tidal marsh, floodplain storage, and floodplain habitat functions — to support the flora and fauna native to the Chelsea Wetlands in the riparian zone and the bottom land tidal flood plain.[2][1][3][4]