Water Quality Threshold

“. . . the water was not merely transparent, but dazzlingly, brilliantly so.”
- a description of Lake Tahoe by Mark Twain, Roughing It (1871)

The focus of the League to Save Lake Tahoe is water quality and clarity in Lake Tahoe. The clarity of Lake Tahoe was first made famous by Mark Twain in the 1880s. Tragically, the pristine clarity of Lake Tahoe as experienced by early visitors is no more. Consistent scientific measurements of water clarity started in 1968. At that point, one could see a white disk submerged to a depth of 100 feet. Today, clarity has dropped to around 70 feet. That means Tahoe is losing about one foot of clarity per year.

Why is Tahoe losing clarity?

Recent water quality research has shed more light on the causes of the decline in lake clarity.  Lake Tahoe is experiencing a phenomenon known as cultural eutrophication—excessive algal growth due to excessive nutrient levels. Nitrogen and phosphorus from automobile emissions and urban and forested areas act like fertilizer to accelerate algal growth.

Aside from the negative impacts of nitrogen and phosphorus, scientists have identified fine sediments as the primary source of lake clarity loss. Fine sediments are tiny, ground up particles—much smaller than the width of a human hair. These fine sediments enter the lake from roadways and urban areas. Rather than falling to the bottom of the lake, fine sediments remain suspended in the water column, making the shoreline areas appear murky and brown.

The consensus among scientists is that we need to drastically reduce the amount of pollution entering the lake to stop or reverse Lake Tahoe’s clarity loss. “Charting a Course to Clarity" is a concise, readable document that addresses which pollutants are causing Lake Tahoe to lose clarity, how much pollution is entering Lake Tahoe, how much pollution the Lake can absorb and still restore clarity, and the options for reducing pollution.

For 60 years the League has been an advocate for strong measures to protect the Lake. We support solutions such as developing an effective public transportation system, restoring natural wetlands and streams, implementing strong erosion control measures, and regulating the rate of development. In addition, we work to educate residents and visitors about opportunities to take action and help restore the environment.