Those colorful waters pictured above can often be seen during final approach to the San Francisco and Oakland airports. They are salt ponds, part of the Don Edwards San Francisco Bay National Wildlife Refuge. The ponds actually produce salt for a wide range of commercial uses. The vibrant hues have to do with the aquatic life that thrives on the ever increasing salinity levels as the ponds dry and concentrate in the sun.
The refuge is over 30,000 acres of protected wetlands around the southern perimeter of San Francisco Bay. Millions of birds, over 250 species, use the area permanently or during migration. Included within the refuge are 9,000 acres operated by Cargill Salt. They use the Bay salt water and a vast network of drying/concentrating ponds to process salt naturally using solar energy to slowly leech the salt from the ocean water. In the process higher and higher concentrations of salinity are achieved in the evaporation ponds, this process gives rise to marine life in the form of brine shrimp and blue-green algae, which attract a wider range of marine birds than would not be attracted to the uniform concentration of naturally occurring ocean water. It is one of these algaes, Dunaliella, that changes to the brilliant red or vermillion color when the salt content of the water reaches high levels.
Eventually, the water is baked away by the sun and the salt and other minerals are harvested. Commercial uses include: road salt, home soft water conditioners and eventually after a final cleansing process -- table salt. If you have Diamond Crystal salt in your kitchen, this is where it comes from.
Cargill has an interesting virtual tour of the process on its website.
If you happen to live in the Bay Area or are in town for a conference, you can visit the Wildlife Refuge and tour the salt ponds.
