Lake Tahoe in California is known for its bluish color and for some time, people thought that the water's bright blue color can be attributed to it being so clear. A new study, however, revealed that something else is responsible for making Lake Tahoe very blue.

The new study conducted by researchers from the University of California Davis found that when Lake Tahoe's color intensified, it was not when the lake was its clearest. It was in fact the opposite as the lake tends to get less blue when it is clearer and the color blue gets deeper when the lake was less clear.

Reporting their findings in the "Tahoe: State of the Lake Report 2015," on July 23, the researchers revealed that the iconic blueness of Lake Tahoe is strongly associated with algae and not clarity as earlier believed with the researchers finding that the lake tends to be bluer when it has lower algal concentration.

Shohei Watanabe, from UC Davis, and colleagues came up with the idea of a Blueness Index to measure what factors contribute to the brilliant color of Lake Tahoe. They used data from a research buoy of the NASA Jet Propulsion lab that captures light.

With the Blueness Index, the researchers found that the lake is bluer with lower algal concentration and that blueness and clarity are separate.

The researchers reported that sediment controls clarity while algal concentration controls blueness, which is driven by the level of nutrients such as phosphorus and nitrogen that are available to the algae. The lake appears bluer with less nutrients and less algae. Drought reduces the flow of water along with nutrients and sediments that enter Lake Tahoe from creeks and rivers, which create the perfect condition for a very blue lake.

Watanabe, however, noted, that clarity should not be disregarded as their findings revealed that nutrient inputs and the concentrations of algae should be managed more closely in order to keep Lake Tahoe blue and clear.

"This is good news," said UC Davis Tahoe Environmental Research Center director Geoffrey Schladow. "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."

Photo: Don Graham | Flickr

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