 Its mouth lies near the north end of the Gulf of the Farallones National Marine Sanctuary.California's 1994 water quality report designated all of Americano Creek and most of the Estero Americano as "impaired" streamways as defined in section 303(d) of the Federal Water Resource Statutes, due to runoff from pasture land and feedlots.As recently as 1987, a single gully near Americano Creek released 4,000 tons/year of sediment, contributing to flooding in downstream communities and making the creek non-navigable.