Keeping Tahoe Blue Doesn't Mean Keeping Clear

From Conservation Magazine:

The Amazon River and its tributaries, long watery snakes wind their way through the Amazon rainforest, are a dull, murky, muddy brown. Other waterways show up as green, primarily thanks to photosynthesizing algae. But perhaps the most prized waterways are colored a deep, rich, vibrant blue. Lake Tahoe, the second deepest lake in the US and sixth largest (following the five Great Lakes), is one of the most iconic blue water lakes.

For a long time it’s been thought that the lake’s prized blueness, the focus of local “Keep Tahoe Blue!” campaigns, was related to water clarity. That makes intuitive sense. But the latest State of the Lake, a yearly publication from UC Davis’s Tahoe Environmental Research Center (TERC), reports something different. For the first time ever, researchers there have managed to quantify the lake’s blueness by developing a measurement they call the “blueness index.”

To measure the lake’s blueness, TERC postdoctoral researcher Shohei Watanabe collaborated with researchers from Canada’s Laval University and NASA-JPL to measure the wavelengths of visible light leaving the water. By continuously monitoring those wavelengths, he was able to create a color record over time for the lake.

But it turns out that during parts of the year when clarity increases, blueness actually decreases. Clear water does not a blue lake make.

The lake’s clarity is governed by the presence (or absence) of fine particulate matter that seeps into the lake from the surrounding land. When there are fewer particles floating around, the lake becomes clearer – but not bluer. Blueness, instead, is related to the presence of algae. When there are more algae, the lake appears less blue to the human eye.

Learn more here: http://conservationmagazine.org/2015/07/keeping-lake-tahoe-blue-doesnt-mean-keeping-it-clear/