Salt evaporation pond

San Francisco Bay salt ponds

Salt evaporation ponds are shallow man-made ponds designed to produce salt from sea water. The seawater is fed into large ponds and water is drawn out through natural evaporation which allows the salt to be subsequently harvested. The ponds also provide a productive resting and feeding ground for more than 70 species of waterbirds, including several endangered species. The ponds are commonly separated by levees.

Due to variable algal concentrations, vivid colors, from pale green to bright red, are created in the evaporation ponds. The color indicates the salinity of the ponds. Micro-organisms change their hues as the salinity of the pond increases. In low to mid-salinity ponds, green algae are predominant. In middle to high salinity ponds, an algae called Dunaliella salina shifts the color to red. Millions of tiny brine shrimp create an orange cast in mid-salinity ponds. Other bacteria such as Stichococcus also contribute tints. These colors are especially interesting to airplane passengers or astronauts passing above due to their somewhat artistic formations of shape and color.

Notable salt ponds include the San Francisco Bay salt ponds in the United States,India and the Dead Sea salt ponds in Israel and Jordan and Useless Loop, and Onslow, Western Australia. Abandoned salt pans are a major feature of the southwest coast of Taiwan.

Salt pans are shallow open pans used to evaporate brine for the production of salt. The pans are usually found close to the source of the salt. For example pans used in the solar evaporation of salt from sea water are usually found on the coast, whilst those used to extract salt from solution mined brine will be found near to the brine shaft. In this case extra heat is often provided by lighting fires underneath.