Three months ago, Iran's Lake Urmia was green. Today, it's blood red. But it's not something that's been added to the lake that caused the change — it's something that's been taken out. Lake Urmia, before and after (Image: NASA Earth Observatory images by Joshua Stevens)
NASA's Earth Observatory caught the lake in transition, photographing it first in April, when it was a springtime green and again last week it's in current red tone. Thanks to the incredibly dry summer, the water levels in the lake are dropping. So although there's a lot less lake, there's just as much salt. The higher salinity of the water caused a red algae bloom, instead of the green one we saw before.
You can see this occur in other lakes, as well. In fact, Utah's Great Salt Lake, which is separated in the middle by a railroad causeway, gives a literal side-by-side comparison of the phenomenon.
Great Salt Lake (Image: Astronaut photo from the ISS/NASA/JSC)
It's likely to be a temporary change. Lake Urmia has turned red in the past and gone back to green during wetter seasons. But, NASA also notes the possibility that, as Iran's drought increases, red could eventually be Lake Urmia's permanent shade.