Flying in or out of the Bay Area, you may have noticed San Francisco Bay’s colorful salt ponds from above.

Otherwise, many of the ponds, which cover approximately 16,500 acres of the bay and have been used as salt evaporation ponds since the California Gold Rush era, remain a hidden secret.

Most of the ponds were once wetlands in Newark, Hayward and Redwood City. Some are no longer in use, but Cargill Salt continues its operations in Newark. The salt the company produces is used to manufacture glass, paper, plastic, rubber, textiles, dyes, leather, cosmetics and pharmaceuticals. The Cargill plant is capable of crystallizing 500,000 tons of sea salt each year.

After nearly a century of commercial land use, 15,000 acres of salt ponds were set aside in 1979 to create the Don Edwards San Francisco Bay National Wildlife Refuge.

State and federal wildlife agencies also acquired 15,100 acres of South Bay salt pond properties in San Jose’s Alviso district, Union City and Menlo Park in 2003, launching the South Bay Salt Pond Restoration Project, the largest wetland restoration project on the West Coast, which will be a 50-year effort.

Last April, in what environmental groups are hailing as a “complete victory,” Cargill Salt announced that it will not appeal a decision by a federal judge that protects Redwood City’s salt ponds from development, effectively halting its decades-long effort to build thousands of new homes there. The project would have been the largest development on the bayfront since Foster City was built in the 1960s.

The pond’s vibrant colors come from algae and microorganisms that live in the ponds, and they differ in hue based on the salinity of the water.

Staff writer Aldo Toledo contributed to this report.

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