Lake Tahoe's average clarity increased substantially in 2011, but the annual measurement indicating the lake's general health was a tale of two seasons.
The average Secchi depth for the lake was 68.9 feet in 2011, an improvement of 4.5 feet over 2010, according to the UC Davis Tahoe Environmental Research Center's 2012 State of the Lake Report, released Thursday.
Secchi depths are gathered by lowering a dinner-plate sized white disc into the lake and recording when the plate is no longer visible to observers. Lake Tahoe's Secchi depth was 102.4 feet in 1968.
The gains in average annual clarity came …