“A noble sheet of blue water,” Mark Twain wrote of Lake Tahoe in 1871, “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. Or it did, anyway. For decades, as Lake Tahoe gradually became murkier, scientists have struggled to understand why. In the 1960s, visibility through the waters of Lake Tahoe was about 90 feet; by the early 2000s it was down to 60 feet, according to NASA, which has monitored the lake’s environment using buoys rigged up to satellites since 1999. (The buoys are also in place to help NASA make sure its satellite measurements are calibrated properly.)
Worse clarity, many assumed, would make for a less vibrant blue.
Scientists now believe they understand a key component of what gives Lake Tahoe its colorful pop. It isn’t the clarity, but a lack of algae that makes for the distinctive color. Even more surprising: Clarity and blueness seem to be at odds with one another. Scientists at the University of California at Davis included the first-ever “quantification of Tahoe’s blueness,” based on measuring of the wavelength of light coming from the lake, in this year’s State of the Lake report.
“While water clarity and lake blueness have long been considered to be one and the same, a newly developed Blueness Index has shown that this is not the case,” they wrote. “On the contrary, at times of year when clarity increases, blueness is seen to decrease.”