Why Lake Tahoe is So Blue: Scientists Discover Blueness is Not from Clarity

First Posted: Jul 28, 2015 09:16 AM EDT

Why is Lake Tahoe so blue? That's a good question and now, scientists have the answer. It turns out that the blueness of Lake Tahoe isn't due to its clarity, but rather is related to algae.

Many assume that lake clarity is tied to its "blueness." This thought, in part, is largely what has driven advocacy and management efforts in the Lake Tahoe Basin for decades. This latest study, though, shows that at times of the year when clarity increases, blueness actually decreases and vice versa. This is largely due to the seasonal interplay of sediment, nutrients and algal production as the lake mixes.

In this latest study, the researchers created a Blueness Index, which quantifies Lake Tahoe's color by using data from a NASA-JPL research buoy at the lake and hyperspectral radiometers that measure the amount of light leaving the lake at each waveband. The scientists then combined the Blueness Index with clarity measurements. In the end, the researchers found that clarity did not correspond with blueness. In fact, they varied in opposite directions.

"This is good news," said Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center, in a news release. "It shows that we better understand how Lake Tahoe works, and it reinforces the importance of controlling nutrient inputs to the lake, whether from the forest, the surrounding lawns or even from the air. It's particularly encouraging that blueness has been increasing over the last three years."

This doesn't mean that clarity should be dismissed, of course. Instead, it shows that algae concentrations and nutrient input should be managed more closely to truly keep Tahoe blue and clear.

The findings reveal a bit more about Lake Tahoe and show that when it comes to how blue the water is, clarity isn't the only thing in play.

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