Lake Tahoe’s famously blue waters are maintaining their overall clarity, despite dropping 5 feet last year.
The findings, released by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional Planning Agency, reported the average annual clarity level at 70.1 feet in 2013, a 5-foot decrease from the previous year but still above recent averages.
The annual State of the Lake report was released Thursday.
Clarity level is arrived at by taking an average from 25 readings taken at different times of the year. The deepest clear depth reading in 2013 was 90 feet, and the lowest was 49 feet.
The lake is generally less clear during months when runoff brings sediment into the water, but last year’s low precipitation reversed that trend. The report found that summer clarity is declining, although still better than the worst years.
Clarity is measured by the depth at which a 10-inch white disk, called a Secchi disk, remains visible underwater. Clarity measurements at Lake Tahoe have been recorded since 1968, when the Secchi disk could be seen at a depth of 102.4 feet.
Maintaining the lake’s clarity is mandated by state and federal agencies, which have set a restoration target of 97.4 feet. A region-wide program to monitor and mitigate urban stormwater runoff has helped stabilize Tahoe’s clarity, officials said.
“The long-term clarity trend is good news, and it tells us that the investments being made on roadways and properties to infiltrate storm water are working,” said the planning agency's executive director, Joanne Marchetta.
Clarity readings since 1997:
* 2013: 70.1 feet
* 2012: 75.3 feet
* 2011: 68.9 feet
* 2010: 64.4 feet
* 2009: 68.1 feet
* 2008: 69.6 feet
* 2007: 70.1 feet
* 2006: 67.7 feet
* 2005: 72.3 feet
* 2004: 73.6 feet
* 2003: 70.9 feet
* 2002: 78.0 feet
* 2001: 73.6 feet
* 2000: 67.4 feet
* 1999: 69.0 feet
* 1998: 66.1 feet
* 1997: 64.1 feet
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