Pool of Blood: Lake in Iran Turns Red in Summer

​The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite recently captured a transition in the color of Lake Urmia between April and July 2016. On April 23, the water was green as usual; by July 18, the lake started to look more like a wine spill.

​Like the Aral Sea, once the fourth largest salty lake, Lake Urmia has shrunk rapidly during the past decades. The results from satellite imagery indicated that the lake has lost about 70% of its surface area over the last 14 years, scientists say. As it becomes smaller, it grows saltier, especially during the summertime. That is when the microorganisms show their colors.

According to scientists, there are two main groups of organisms involved in the color change: a family of algae called Dunaliella and an archaic family of bacteria known as Halobacteriaceae.

​

"In the marine environment, Dunaliella salina appears green; however, in conditions of high salinity and light intensity, the microalgae turns red due to the production of protective carotenoids in the cells," explained Mohammad Tourian, a scientist at the University of Stuttgart. Carotenoids are organic pigments responsible for bright red, yellow and orange hues.

Other scientists emphasize the role of Halobacteriaceae, a group of bacteria, which release a red pigment that absorbs light and converts it into energy for the bacteria. When populations of the bacteria are large enough, they can stain bodies of water.