Lake Tahoe, CA/NV – Lake Tahoe’s clarity improved in 2012 for the second year in a row, and its waters
were the clearest in 10 years, according to University of California, Davis, scientists who study the lake.
Last year’s average annual clarity level was 75.3 feet, or a 6.4-foot improvement from 2011, according to
data released today by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional
Planning Agency.

The lake’s clarity is measured by the depth at which a 10” white disk, called a Secchi disk, remains visible
when lowered beneath the water’s surface. The measurements have been taken since 1968, when the
Secchi disk could be seen down to an average of 102.4 feet.

The annual clarity level is the average of 22 individual readings taken throughout the year. The highest
individual value recorded in 2012 was 107 feet, and the lowest was 57 feet.

Researchers provided measurements for last year’s winter (Dec.–Mar.) and summer (Jun.–Sept.)
months. Winter clarity last year continued a long-term pattern of improvement, with the best clarity
since 1996. The winter average of 88.3 feet in 2012 was well above the worst point seen in 1997 and a
combined 12-foot improvement for the past two years.

At 64.4 feet, summer clarity improved 13 feet from the 2011 value, but researchers say the persistent
trend is still one of declining summer clarity.

“The improvement we see in both the summer and winter clarity during 2012 is very encouraging,” said
Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center. “The lake will
continue to be subjected to a range of disturbances, each of which has the potential to impact clarity.
There is now growing belief that managing for clarity is possible.”

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