Lake Tahoe's iconic blueness is most strongly related to algae, not clarity, according to research released today from the UC Davis Tahoe Environmental Research Center, or TERC. In the "Tahoe: State of the Lake Report 2015," researchers found the lower the algal concentration, the bluer the lake. The report also includes updates related to clarity, climate change, drought and new research at Lake Tahoe. 

CLEAR AND BLUE

The assumption that lake clarity is tied to blueness has driven advocacy and management efforts in the Lake Tahoe Basin for decades. But the report's findings show that at times of the year when clarity increases, blueness decreases, and vice versa. This is due to the seasonal interplay of sediment, nutrients and algal production as the lake mixes.

Clarity is controlled by sediment. Blueness is controlled by algal concentration, which in turn is driven by the level of nutrients available to the algae.

"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." 

Low precipitation helped keep runoff from both nutrients and sediment low in 2014.