I knew that such salt ponds existed, but I've never seen any and I thought they're used mostly in some exotic country. Thanks to this card, I learned that they can be found also in Europe :) By the way, I didn't know that it was possible to produce so much salt of sea water... But I think Baltic Sea isn't saline enough and evaporation would take too long in our climate, that's why there are no salt ponds in Poland.
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.