This indicator measures the concentration of suspended sediment in surface runoff. In an undisturbed watershed, the majority of stormwater is captured by vegetation and absorbed and filtered through the soil. Development, such as roads, driveways, and rooftops alter the watershed by creating impervious surfaces that prevent stormwater from infiltrating. Instead, stormwater runs over impervious surfaces, collecting pollutants such as suspended sediment as it travels, enters the nearest storm drain or stream, and ultimately ends up in Lake Tahoe. Pollutants, including suspended sediment, contribute to the decline in lake clarity. Landscape modification (e.g., impervious cover such as roads or residential and commercial development) influences the volume of runoff, erosion rates, and the ability of the watershed to retain sediment and nutrients. Urban growth control limits, best management practices (BMPs) to reduce nutrient and sediment discharge from disturbed soils, BMP retrofit regulations for developed properties, and limits on coverage all help to reduce suspended sediment from surface runoff. The Lake Tahoe TMDL is the Region’s science-based strategy to reduce pollutant loading to Lake Tahoe and restore the historic clarity of the lake.


Evaluation Map

Lake Clarity Tracker Projects

2019 Evaluation

Insufficient Data to Determine Status or No Target Established
Rapid Improvement
View Evaluation

Applicable Standard

WQ22: Achieve a 90 percentile concentration value for suspended sediment of 250 mg/l in surface runoff directly discharged to a surface water body in the Basin.

Key Points

  • In 2019, TMDL implementors (CalTrans, CLST, Douglas, El Dorado, NDOT, Placer, Washoe) exceeded all pollutant load reduction targets and collectively reduced average fine sediment particle concentrations in surface runoff by 19.7 percent from baseline levels.
  • The targets for surface runoff and groundwater discharge articulated in water quality threshold standards (standards 19-32) were designed to reduce pollutant load and improve ambient water quality. The TRPA Code of Ordinances provides specific direction to ensure that activities and development in the Region are compatible with the Regional Plan and support the attainment and maintenance of the Region’s shared goals for restoration and environmental quality as expressed in the threshold standards.
  • The Tahoe Science Advisory Council recommends that discharge standards WQ19-WQ32 are not suitable for threshold standards, but should be retained in the TRPA Code (currently at Chapter 60) as management restrictions on discharge.

Delivering and Measuring Success

Lake Clarity Indicators

  • Fine Sediment Load Reduction

    TMDL urban implementing partners have acheived greater than total fine sediment load reduction targets required by permits and agreements

Monitoring Programs

  • Regional Stormwater Monitoring

    The Regional Stormwater Monitoring Program measures pollutants in urban runoff to evaluate the effectiveness of pollutant control measures and track and report monitoring findings.