Did you know … Scientists have been measuring Tahoe water clarity since 1968?
Scientists have been measuring Tahoe water clarity by lowering a 10-inch white disk into the lake since 1968.
Called a Secchi depth test, researchers record the maximum depth before the disk disappears from view.
Annually, scientists take about 25 readings throughout the year.
While researchers have observed increasing clarity in some years, on average visibility has been dropping by one foot per year since the 1960s.
Depths of over 120 feet were recorded in the early years, but in 2006, visibility had dropped to an average 67.7 feet, a reduction of 4.6 feet from the year before.
Tahoe’s low point for clarity so far came in 1997 at 64 feet.
Years with high runoff wash larger amounts of material detrimental to lake clarity, predominantly nutrients and fine sediments, into Lake Tahoe.