Big River Estuary, located near Mendocino on California's north coast, is one of the longest tidal estuaries in the state, stretching approximately 8 miles inland from the Pacific Ocean. This dynamic system is shaped by the interaction of freshwater from the Big River watershed and tidal flows, creating a rich mosaic of habitats, including mudflats, salt marshes, and riparian forests.

The estuary thrives in the region's cool, foggy coastal climate, with wet winters and dry summers influencing water levels and salinity. It supports diverse wildlife, including steelhead trout, coho salmon, river otters, and migratory birds, while the surrounding wetlands play a vital role in water filtration and carbon storage. Protected as part of Mendocino Headlands State Park, Big River Estuary is not only an ecological treasure but also a popular spot for kayaking, hiking, and wildlife observation. Conservation efforts focus on preserving its natural processes and enhancing habitat resilience in the face of climate change.