Lake Tahoe's clarity shows gains for a second year

02/28/2013 12:00 AM

02/27/2013 11:45 PM

The crystal blue waters of Lake Tahoe are getting more transparent.

The clarity of the alpine lake improved for the second consecutive year, according to UC Davis researchers. The lake's waters are the clearest in 10 years, they said.

In 2012, the lake's average annual clarity level was 75.3 feet – a 6.4-foot improvement over the previous year, according to information released Wednesday from the university's Tahoe Environmental Research Center and the Tahoe Regional Planning Agency.

"It is particularly encouraging to see clarity improve during wet years when the amount of fine sediments and nutrients going into the lake is high," said John Reuter, associate director of the UC Davis research center.

Scientists measure the lake's clarity by the depth at which a 10-inch disk remains visible when lowered beneath the water's surface. When the so-called Secchi disk was first used in 1968, it could be seen down to 102.4 feet.

Lake clarity degradation followed that measurement and steps have been taken to try to prevent cloudy water conditions.

Urban storm water runoff is a contributor to reduced clarity at the lake. Storm water, especially in the winter and spring, carries inorganic particles from undeveloped and developed land.

Efforts to reduce storm water runoff might be having a positive impact on lake clarity, but more data is needed to confirm that possible conclusion, scientists believe.

– Bill Lindelof

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