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Lake Tahoe Programs

Lake Tahoe is a designated Outstanding National Resource Water (ONRW) that is renowned for its extraordinary clarity and purity, and deep blue color. Since the late 1960s, Lake Tahoe has become impaired by declining deep water transparency (clarity) and increasing phytoplankton (algae) productivity due to increased fine sediment particles (FSP) and nutrient loading attributable to human activities.

Steep slopes, erodible soils, and a short growing season make the Lake Tahoe Basin acutely sensitive to human activities. Development practices and ongoing soil disturbing land uses that may have little impact elsewhere can cause severe erosion in the Tahoe Basin, increasing FSP, nitrogen and phosphorus loads delivered to the lake. FSP directly reduces water transparency because particles are held in suspension in the water and scatter light; the nutrients nitrogen and phosphorus increase algae growth which in turn also contributes to loss of water transparency and water color.

Human development disturbs vegetation and soils and creates impervious surface coverage that interferes with natural nutrient and FSP removal mechanisms. Runoff from roadways and other urbanized landscapes are the primary sources of FSP reaching the lake. Increased growth of attached algae in nearshore waters may be linked to the level of onshore development. Other sources of nutrients include fertilizers, sewer leaks and leachate from abandoned septic systems, and atmospheric deposition.

In 2011, the California Water Boards together with the Nevada Dept. of Environmental Protection (NDEP) adopted the Lake Tahoe Total Maximum Daily Load (TMDL) to address FSP and nutrient loading and restore deep water transparency. To achieve the goals of the TMDL and restore lake water quality, nutrients and sediment loads to the lake must be reduced by addressing a variety of point and nonpoint sources, including solid and liquid waste disposal, road maintenance, construction, and stormwater management.

As well as Lake Tahoe, there are 170 other lakes, 63 tributary streams, and numerous wetlands in the Lake Tahoe Basin; most of the lakes and about half of the streams are in California. There are also two named ground water basins in the California portion of the watershed. Most of these waters are naturally of high quality, and although many are within wilderness areas, they are threatened by heavy recreational use and atmospheric deposition. Other tributary waters have been adversely affected by erosion, stormwater, diversion, channelization, or filling. In particular, wetlands have been drastically disturbed by human activities.

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