Estero de San Antonio is a small coastal lagoon formed by a sandbar damming Stemple Creek, located 5.75 miles (9 km) southeast of the community of Bodega Bay and 1.5 miles (2.4 km) northwest of Dillon Beach, California. This stream begins in the hills of Marin and Sonoma Counties and flows generally west to Bodega Bay, near the mouth of Tomales Bay. In some years, the seasonal sandbar at the mouth of Stemple Creek entirely restricts tidal exchange, leading to periods of hypersalinity in the estuary. When the mouth is open, tidal influence can extend upstream for 4 miles (6.5 km).

The Coast Miwok historically inhabited the beaches along the river mouth. From the start of European settlement in 1865, the watershed supported mixed farming, with small livestock herds and large areas cultivated for barley, wheat, vegetables, and potatoes. Poultry and egg production played a vital role in the local economy from the 1930s through World War II. In 1977, the California Department of Fish and Game identified the Estero de San Antonio as one of the state’s most significant habitat areas. The watershed features a mosaic of habitats, including densely wooded riparian ravines, salt grass flats, mudflats, eelgrass beds, small freshwater ponds, and coastal oak woodlands in the upper watershed. Today, 90% of the watershed is used for livestock grazing, primarily beef and sheep ranches in the Marin County portion, with a few dairies.

Estero de San Antonio State Marine Recreational Management Area is a protected zone covering 0.09 square miles (23 ha). It includes the waters below the mean high tide within the lagoon and is part of the Greater Farallones National Marine Sanctuary. The area prohibits the taking of any living marine resources, preserving its biodiversity. Access to the beach is exclusively by boat, as private property restricts land access. Read more here and here. Explore more of Estero de San Antonio and Bodega Bay here: