In the 1960s plans to fill the bay’s tidelands for development stirred local activists to push for protection of the south Bay’s marshes and salt ponds. The refuge was founded in 1974, the first urban national wildlife refuge in the United States, and from 1977 through 2003 it grew with salt ponds bought from Cargill.
By 2004 it covered about 30,000 acres of open bay, salt pond, salt marsh, mudflat and upland, part of it within San Jose near Alviso. About 9,000 acres of salt ponds are still worked by Cargill, which has permanent salt-making rights. The refuge lies on the Pacific Flyway, and protecting migratory birds is one of its purposes.