The latest scientific findings from Lake Tahoe show a trend toward long-term water clarity.
Clarity levels at the alpine lake continued to stabilize in 2013, according to University of California, Davis scientists. The average clarity reading for last year was 70.1 feet.
Even though that reading was 5 feet less that the previous year, it is much better than the reading recorded in 1997 of just 64.1 feet and above more recent years’ averages.
The clarity level is arrived at by taking the average of 25 readings. The best reading last year was 90 feet, the worst 49 feet.
“Clarity in Lake Tahoe largely reflected what we saw in the weather in 2013,” said Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center. “At the beginning of the year, clarity was lowered by large stream inflows. At the end of the year, the low inflows resulting from the drought conditions helped to improve clarity.”
Water clarity is measured by the depth at which a 10-inch disk lowered into Lake Tahoe can been seen. Such measurements have been taken since 1968 when the disk could be seen down to 102.4 feet, according to a UC Davis press release.
Scientists say the average annual clarity in the past decade has been better than in preceding decades, but it is still short of a target clarity of 97.4 feet set by federal and state regulators.
Urban storm water runoff is believed to be the major contributor to reduced clarity at the lake.
“Through the seasonal and annual fluctuations, the long-term clarity trend is good news, and it tells us that the investments being made on roadways and properties to infiltrate stormwater are working,” said Tahoe Regional Planning Agency executive director Joanne Marchetta.
Clarity readings through the years:
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