Between April and July, Iran's salty Lake Urmia changed from a bright green color to a blood red. NASA's Aqua satellite captured the image above and reported on the science behind the strange transformation. According to NASA, the periodic color change is caused by micro algae producing carotenoids that help with photosynthesis and act as antioxidants and Halobacteriaceae, a bacteria in very salty water that releases "a red pigment called bacteriorhodopsin that absorbs light and converts it into energy for the bacteria." From NASA:
The color changes have become common in the spring and early summer due to seasonal precipitation and climate patterns. Spring is the wettest season in northwestern Iran, with rainfall usually peaking in April. Snow on nearby mountains within the watershed also melts in the spring. The combination of rain and snowmelt sends a surge of fresh water into Lake Urmia in April and May. By July, the influx of fresh water has tapered off and lake levels begin to drop.
The fresh water in the spring drives salinity levels down, but the lake generally becomes saltier as summer heat and dryness take hold. That’s when the microorganisms show their colors, too. Careful sampling of the water would be required to determine which organisms transformed the lake in 2016, but scientists say there are likely two main groups of organisms involved: a family of algae called Dunaliella and an archaic family of bacteria known as Halobacteriaceae.
While Lake Urmia has shifted from green to red and back several times in recent years, trends suggest that a red Urmia could become increasingly common. Drought and intensive water diversion for agriculture has been limiting the amount of fresh water reaching the lake. “The lake volume has been decreasing at an alarming rate of 1.03 cubic kilometers per year,” noted Tourian, who recently analyzed data from several satellites to track how Urmia has changed. “The results from satellite imagery revealed a loss of water extent at an average rate of 220 square kilometers per year, which indicates that the lake has lost about 70 percent of its surface area over the last 14 years.”