Estero Mantagua is a coastal estuary located in the Valparaíso Region of Chile, flowing toward the Pacific coast. The estuary sits within a biologically significant area near the mouth where freshwater and saltwater mix, creating a dynamic environment that supports a variety of wildlife. The surrounding riparian zone features native coastal vegetation, and the estero's lower reaches near its desembocadura (mouth) are recognized as habitat for rare and endemic species, reflecting the ecological richness of this part of central Chile's coastline.