Molecular Diffraction

My wife and I took a short get-a-way to Lake Tahoe in the high Sierras. 
It's famous for its blueness.  A noble sheet of blue water,” Mark Twain wrote of Lake Tahoe, “As it lay there with the shadows of the mountains brilliantly photographed upon its still surface, I thought it must surely be the fairest picture the whole earth affords.”  

The striking hue is one thing, but Tahoe also has splendid clarity.  Visibility through the waters of Lake Tahoe are about 60 feet. It isn’t the clarity, but a lack of algae that makes for the distinctive color.