In 2013, Lake Tahoe lost 5 feet of clarity

Clarity levels within Lake Tahoe decreased 5 feet in 2013, according to data released Thursday by University of California, Davis, scientists who study the lake.

Data compiled by the UC Davis Tahoe Environmental Research Center and the Tahoe Regional Planning Agency shows the average annual clarity level for 2013 was 70.1 feet. The average level in 2012 was 75.3 feet, while it was 64.1 feet in 1997, the year it was at its lowest.

The clarity level this year is the average of 25 individual readings taken throughout the year, according to a news release from UC Davis. The highest individual value recorded in 2013 was 90 feet, and the lowest was 49 feet, due to seasonal variations.

“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, in a statement. “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.”

Clarity is measured by the depth at which a 10-inch white disk, called a Secchi disk, remains visible when lowered beneath the water’s surface. The measurements have been taken continuously since 1968, when the Secchi disk could be seen down to 102.4 feet.

Information about environmental factors affecting Lake Tahoe will be included in the 2014 State of the Lake Report, expected this summer.

Funding for TERC’s clarity analyses comes from the Tahoe Regional Planning Agency.