Salt evaporation ponds formed by salt water impounded within levees in former tidelands on the shores of San Francisco Bay. There are many of these ponds surrounding the South Bay. As the water evaporates, micro-organisms of several kinds come to predominate and change the color of the water. First come green algae, then darkening as orange brine shrimp predominate. Finally red predominates as dunaliella salina, a micro-algae containing high amounts of beta-carotene (itself with high commercial value), predominates. Other organisms can also change the hue of each pond. Colors include red, green, orange and yellow, brown and blue. Finally, when the water is evaporated, the white of salt alone remains. This is harvested with machines, and the process repeats.