Elkhorn Slough is a 7-mile-long (11Â km) tidal slough and estuary on Monterey Bay in Monterey County, California. It is California's second largest estuary and the United States' first estuarine sanctuary. The community of Moss Landing and the Moss Landing Power Plant are located at the mouth of the slough on the bay. The Elkhorn Slough National Estuarine Research Reserve and Elkhorn Slough State Marine Conservation Area (SMCA) are in the area.
Elkhorn Slough harbors the largest tract of tidal salt marsh in California outside the San Francisco Bay and provides much-needed habitat for hundreds of species of plants and animals, including more than 340 species of birds. It has been designated as a protected Ramsar site since 2018.