Keep Tahoe Blue: Measuring a Fading Clarity
Near Tahoe City, California
Lake Tahoe's famous blue is not just beautiful, it is measured. Since nineteen sixty-eight, scientists at the University of California, Davis have lowered a white disk, called a Secchi disk, into the water and recorded the depth at which it disappears from view. Around nineteen sixty-eight, that disk stayed visible to just over one hundred feet down.
In recent years the annual average has hovered closer to seventy feet. The decline came from the growth of nearby towns and ski resorts, as road dust, fertilizer, and disturbed soil washed fine particles and nutrients into the lake, feeding tiny algae and clouding the water. The decline fed one of the country's earliest environmental movements.
The League to Save Lake Tahoe, whose Keep Tahoe Blue bumper stickers you have surely seen, formed in nineteen fifty-seven to fight unchecked development. In nineteen sixty-nine, California and Nevada jointly created the Tahoe Regional Planning Agency to govern the whole basin across two states. Thanks to decades of that work, the long slide in clarity has largely leveled off, and some recent years have even shown modest gains.
The lake you are looking at is clearer than it would have been without that fight, but keeping Tahoe blue remains very much a work in progress.
