Lake Tahoe's deep cobalt blue color is of great ecological and economic value and a focus for lake management strategies of the region. While water clarity has been scrutinized and routinely measured for more than five decades, the blueness of the lake has never been quantified scientifically, until recently.

In collaboration with NASA-JPL and the Université Laval, Québec, Canada, TERC has developed the blue water index (Bw) to quantitatively express Lake Tahoe's blueness. This objective measurement of water color enables us to conduct continuous monitoring of Lake Tahoe's color as well as the color of other oligotrophic lake waters. 

The color monitoring from 2012 to 2014 revealed that Lake Tahoe's iconic blueness is most closely related to algae, not fine inorganic sediments which is directly correlated to lake clarity.   

The general assumption that lake clarity is tied to blueness has driven advocacy and management efforts in the Lake Tahoe Basin for decades. But these 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.

Development of models estimating lake water blueness from the input of water quality data is currently underway. The model will help us determine past and future lake colors that reflect changing environmental conditions of the region.