Estero Americano Watershed
The Estero Americano is a coastal estuary at the base of Americano Creek; the watershed area is 49 square miles. It forms a portion of the northern boundary between Marin and Sonoma counties where it drains into Bodega Bay. In some years, a seasonal sand bar at the mouth restricts tidal exchange. Periods of hypersalinity have been recorded in the Estero. When the mouth is open, the tidal influence ranges up to 4 miles upstream. Americano Creek, the sole tributary of the Estero, is ephemeral and generally dries up for 4 to 6 months between late spring and fall.
Historically, the watershed was inhabited by Coast Miwok. From 1865 to 1982, the area was used extensively for agriculture, including corn, beets, potatoes, onions, oats, and hay. In the late 1800s, the Estero Americano was reportedly a navigable body of water, and products such as potatoes were shipped to market.
Changes to Watershed Processes
Historic activities in the watershed have contributed excessive amounts of sediment to the Estero. This has changed the shape of the Estero which in turn changes tidal circulation, nutrient circulation, and salinity.
The Estero Americano contains 301 acres of open water and 412 acres of wetland habitat, including mudflats, seasonal brackish marsh, and freshwater marsh. The California Department of Fish and Game (CDFG) identified Estero Americano and its southern neighbor, Estero de San Antonio, as among the most significant habitat areas in the State. Streamside habitat along Americano Creek consists of grazed pastures with few trees interspersed with dense willow thickets. Coastal oak woodland occurs in the upper watershed.
Fish and Wildlife
Special-status species in the watershed include the Northwestern pond turtle, steelhead trout, California red-legged frog, Myrtle’s silverspot butterfly, tidewater goby, and tricolored blackbird have been observed in the watershed.
Other noteworthy species identified in and surrounding the Estero include: 71 species of water and marsh-associated birds, 66 species of terrestrial birds (Madrone 1977 1), and 44 marine and freshwater fish species (Commins et al. 1990 2). Over 70 species of benthic invertebrates and 30 species of epibenthic invertebrates were collected in the Estero in the late 1980s (Commins et al. 1990).
Human Habitation and Land Use
Land Use Imperviousness
Land use within the watershed is primarily dairy operations, beef and sheep grazing, and residences. The small communities of Valley Ford and Bloomfield are within the Sonoma County portion of the watershed.
Restoration efforts in the watershed have included production of the Sonoma County Coastal Wetland Enhancement Plan, an erosion survey of the Estero Americano and several coastal watersheds to the north, was completed in 1987 by Circuit Rider Productions for the Gold Ridge Resource Conservation District (Gold Ridge RCD) (State Coastal Conservancy and Circuit Rider Productions 1987 3). With funding from the State Coastal Conservancy, Gold Ridge RCD undertook repair of many of the erosion sites identified. Gold Ridge RCD continues to be active in the watershed, sponsoring workshops to assist agricultural landowners in developing ranch plans and implementing projects to improve water quality and reduce erosion. More recently, the Gold Ridge RCD produced 2007 The Estero Americano Watershed Management Plan.
In addition, there are significant land conservation efforts in the watershed. The Sonoma County Agricultural Preservation and Open Space District (SCAPOSD) and Marin Agricultural Land Trust (MALT) are both active in the watershed, protecting agricultural land use through conservation easements. The Sonoma Land Trust owns the 127-acre Estero Americano Preserve, which includes salt marsh habitat and some grazing lands.
For more information on the Estero Americano, please contact the Gold Ridge Resource Conservation District at 707.874.2907 or at www.goldridgercd.org
1 The Natural Resources of Esteros Americano and de San Antonio
2 Estero Americano and Estero de San Antonio Monitoring Program: 1988-1989 Results. Long-term Detailed Wastewater Reclamation Studies: Santa Rosa Subregional Water Reclamation System. Draft Technical Memorandum No. E8.
3 Sonoma County Coastal Wetlands Enhancement Plan.