New research reveals Lake Tahoe's brilliant blue hue is thanks to algae growth, and not clear waters.
The assumption that the Sierra Nevada lake's iconic blue waters are caused by its clarity has been the basis of advocacy and management efforts in recent decades, but these recent findings have revealed the opposite is true, the University of California, Davis reported. The study demonstrated that during times of the year when Tahoe's clarity decreases, its blueness increases, suggesting algae and sediment interactions are actually what creates the color.
"This is good news," said Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center and a civil engineering professor. "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."
To make their findings, the researchers created a Blueness Index and combined it with TERC measurements of Secchi depth, which is depth at which a white disk remains visible when it is submerged in the water. The researchers were surprised to find the blueness of the water was inversely correlated with the Secchi measurements.
"This does not mean that clarity should be dismissed," said Shohei Watanabe, a postdoctoral researcher at UC Davis TERC. "Rather, it shows that algae concentrations and nutrient input should be managed more closely to truly keep Tahoe blue and clear."
The findings were published in the most recent State of the Lake report, which "informs nonscientists about the most important factors affecting lake health and helps influence decisions about ecosystem restoration and management within the Lake Tahoe Basin," the researchers reported. The report also outlines changes in climate and drought conditions in the region of the lake.
