As the plane banks to make its final pass before landing at the San Francisco Airport, peeking out of the window will reward you with a view of a vibrantly hued canvas. These configurations of color against the drab shades of the bay are the San Francisco Bay salt ponds.

These bright pond pockets of red and green are caused by the organisms or micro-algae living within them. The microorganisms located in each pond are determined by their tolerance to salinity, and the colors are reactions to salt levels. The evaporation ponds cover an array of hues from bright green, where low salinity encourages green algae to thrive, to a deep coral pink or red hue that is caused by the algae Dunaliella, producing a red pigment in response to high salt content. A high number of tiny brine shrimp cast an orange sheen to the ponds that are considered mid-salinity. Weather can affect the colors as well, but their ever-changing pigments always stand out from the sky, and have served as a visual marker for astronauts.

Since 1854, salt was one of San Francisco’s largest industries, with over 80% of its wetlands developed for salt mining. The salt ponds covered over 16,500 acres, most of which was owned by Cargill, Inc., an international food production and marketing company. In 2003, Cargill, Inc. sold 15,100 acres of the ponds to State and Federal agencies as well as private foundations who are in the process of restoring them to their pristine tidal wetland beginnings.

Now the largest tidal wetland restoration operation on the West Coast, the South Bay Salt Pond Restoration Project is slowly but surely reintroducing bay water to the ponds, and attracting wildlife. While the salt ponds and their beautiful showing may not be there forever, the project is on a 30-year plan, so there’s still some time to enjoy this fading ghost of San Francisco’s industrial history.