Welcome

The Lake Tahoe Total Maximum Daily Load (TMDL) is a science-based plan to restore Lake Tahoe's famous clarity. One of the most robust efforts of its kind, the Lake Tahoe TMDL was initiated to better understand the causes of clarity loss, determine how much pollution needs to be reduced and develop a sensible implementation approach to restore historic clarity. The Lake Tahoe Info Stormwater Tools are used to track Lake Tahoe TMDL implementation progress in urbanized portions of the watershed. Current TMDL implementation achievements are provided in the chart; further context about the tools is provided below the chart.

2016 Program Achievements

Current Achievement Status
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The Lake Tahoe Stormwater Tools include:

  • A road inspection and assessment method and associated tracking system
  • A stormwater treatment BMP inspection and assessment method  and associated tracking system
  • The Lake Clarity Crediting Program credit registration, award, and declaration system

These tools are currently available to users with an account and appropriate system permissions. If you represent an urban jurisdiction or other agency in the Lake Tahoe Basin and need access to the Stormwater Tools please request an account.

The Lake Tahoe Info Stormwater Tools are sponsored by the Lahontan Regional Water Quality Control Board and the Nevada Division of Environmental Protection.

Nevada Department of Environmental Protection

About the Tahoe TMDL

Lake Tahoe is famous for its remarkable clarity and striking blue color. As the largest alpine lake and second deepest in North America, it is designated an Outstanding National Resource Water by the state of California and a “water of extraordinary ecological or aesthetic value” by the state of Nevada. The Lake Tahoe Basin is a destination for millions of visitors annually and is home to approximately 60,000 year-round residents.

Between 1968 and 2000, approximately one-third of Lake Tahoe’s unique clarity was lost. To address this issue, the Lahontan Regional Water Quality Control Board (Lahontan Water Board) and Nevada Division of Environmental Protection (NDEP) collaborated to develop the Lake Tahoe TMDL. The Lake Tahoe TMDL is a science-based plan to better understand the causes of the loss in lake clarity, determine how much pollution needs to be reduced to reinstate historic clarity, and develop a workable, cost-effective implementation strategy. Now in the implementation and tracking phase, controls are being implemented to reduce pollutant loading to Lake Tahoe and Lahontan and NDEP are working closely with project implementers to track progress, report accomplishments, measure effectiveness and adaptively manage implementation efforts.


What Pollutants Are Causing Lake Tahoe's Clarity Loss?

The extraordinary historic clarity of Lake Tahoe is attributed to its extremely clean waters which allow sunlight to reach much greater depths than it reaches in most other water bodies. However, declining clarity over the past half-century is attributable to increased inputs of fine sediment particles (16 microns or less in diameter),  and free floating algae fed by the nutrients nitrogen and phosphorus. Fine sediment particles scatter light, while algae absorb light. As pollutant inputs increase, light is increasingly scattered or absorbed and is unable to penetrate deeper into the water column. Consequently, clarity declines and Secchi depth measurements decrease.


What is the Strategy to Restore Lake Tahoe's Clarity?

Lake Tahoe TMDL science indicates that a 65% reduction in fine sediment particles, accompanied by reductions in nitrogen and phosphorous of 10% and 35% respectively, are necessary to meet the TMDL numeric target of nearly 100 feet. Approximately half these load reductions are needed to meet the Clarity Challenge, an interim milestone of 80 feet annual average Secchi disk depth to be realized by 2031. The Clarity Challenge is an important goal because once attained scientists can state with confidence the trend in clarity loss has been reversed and we are moving toward restoring Lake Tahoe's clarity.

Fine sediment particles have a greater impact on clarity than the algae fed by elevated nutrient concentrations, so although the TMDL program includes required reductions for Total Nitrogen, Total Phosphorus, and fine sediment particles, initial implementation efforts are focused on particle reduction. Furthermore, urban stormwater represents both the greatest source of these particles as well as the greatest opportunity to achieve needed load reductions.  So while the restoration strategy includes efforts to reduce pollutants originating in forests, stream channels and atmospheric deposition, attaining the load reduction goals hinges on reducing fine sediment particles originating in urban areas and transported to the lake through stormwater runoff.