Great Salt Lake, Utah

You see some pretty strange things from 250 miles above the Earth’s surface. This enormous half-purple, half-green body of water is a fine example. 

This orbital view of Utah’s Great Salt Lake reveals a dramatic color change along an oddly precise dividing line. What the high-altitude perspective does NOT reveal is the railroad causeway that cuts the lake in half, effectively turning it into two lakes, each with its own ecosystem. 

Great Salt Lake has no natural outlet, meaning the only escape for its water is through evaporation. Most of the rivers that feed fresh water into the lake enter south of the causeway (right side of image), where salinity fluctuates between 6 and 27 percent. That’s already much saltier than the ocean, but bland compared to the northern section of the lake. Here water evaporates faster than it can be replaced, concentrating the minerals and producing an average salinity of around 30 percent. 

Why purple? The briny conditions are just too harsh for most bacteria. Certain salt-tolerant species with naturally rosy complexions don’t seem to mind, however. 

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