Tahoe’s water clarity failing over time

Located on the ‘bend’ on the California/Nevada border, Lake Tahoe sits in an ancient volcano crater. Cold and surprisingly deep, the high altitude body of water remained much cleaner over the years than most of its lower altitude cousins. The amazing water clarity reached national prominence in 1871 when Mark Twain spoke of it in his book Roughing It. “The water was not merely transparent, but dazzlingly, brilliantly so” wrote Twain.

That clarity is fading, however. Scientific measurements beginning in 1968 showed that one could see a white disk at a depth of 100 feet. By the early 2000’s, that number had dropped to 70 feet. Tahoe is losing roughly one foot of visibility per year with no sign of abating.

Further study has brought to light one of the major culprits of the decline. The lake is experiencing cultural eutrophication – that is, excessive algal growth due to high nutrient levels. Nitrogen and phosphorus from car and truck emissions and urban and forested areas act like fertilizer to accelerate algal growth.

In addition to the negative chemical impacts, researchers have identified fine sediments as the number one cause of the loss of clarity. Tiny, ground up particles – much smaller than the width of a human hair – enter the lake from roadways and neighborhoods. Rather than settling to the bottom of the lake, they remain suspended in the water column, making the shoreline areas murky and brown.

The League to Save Lake Tahoe along with the California State Water Resources Control Boards and the Nevada Division of Environmental Protection produced a guide with strategies and proposed solutions to restoring Lake Tahoe’s pristine clarity. Charting a Course to Clarity can be found on the California Waterboards website.

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