Phosphorus Load (Surface Runoff)
Phosphorus Load in Runoff
Intermediate Result
Kilogram (kg)
1. Reduce total annual nutrient and suspended sediment loads as necessary to achieve loading thresholds for tributaries and littoral and pelagic Lake Tahoe.
2. Tributaries - Reduce total annual nutrient and suspended sediment load to achieve loading thresholds for littoral and pelagic Lake Tahoe.
3. Littoral - Reduce the loading of dissolved inorganic nitrogen, dissolved phosphorus, iron, and other algal nutrients from all sources to meet the 1967 to 1971 mean values for phytoplankton primary productivity and periphyton biomass in the littoral zone.
4. Deep Water (Pelagic) Lake Tahoe - Reduce the loading of dissolved phosphorus, iron, and other algal nutrients from all sources as required to achieve ambient standards for primary productivity and transparency.
Kilograms/year of total phosphorous
This Indicator is reported in the following LT Info areas:

No Subcategories for this Indicator.

Program Regional Stormwater Monitoring


Monitoring is guided by the RSWMP Framework and Implementation Guidance document. During water year 2014 five catchments were monitored for continuous flow and turbidity and sampled for water quality at eleven monitoring stations: the outfalls of the five selected catchments, and the inflows to and outflows from selected BMPs located in three of those catchments. Three additional catchment outfalls were monitored in water year 2015. The catchments were chosen because of their direct hydrologic connectivity to Lake Tahoe, diversity of urban land uses, range of sizes, and a reasonably equitable distribution among the participating jurisdictions. BMP effectiveness sites were selected because of their potential efficacy in treating storm water runoff characteristic of the Lake Tahoe Basin, and the broad interest in, and lack of conclusive data regarding the efficiency of the selected BMPs in reducing runoff volumes and pollutant loads.


Associated Programs data not provided.

View Threshold Evaluation

Phosphorus Load (Surface Runoff) is include in the Threshold Dashboard. Threshold Indicators are evaluated against Threshold Standards every 4 years. Thresholds are environmental goals and standards for the Lake Tahoe Basin that indirectly define the capacity of the Region to accommodate additional land development.


This indicator measures the total phosphorous load delivered to Lake Tahoe and its’ tributaries via direct surface runoff. Nitrogen and phosphorous nutrients are important to the growth and reproduction of plants, and they are considered a pollutant of concern in the Lake Tahoe Basin (Lahontan & NDEP, 2010a). Nitrogen and phosphorus together support the growth of algae in Lake Tahoe (Lahontan & NDEP, 2010a). Free-floating algae (i.e., phytoplankton) occur throughout Lake Tahoe and contribute to the decline in water transparency by absorbing light for photosynthesis. Attached algae (i.e., periphyton) coat rocks in the nearshore, adversely affecting nearshore aesthetics. From an ecological perspective, algae are a dominant component of the aquatic food web, providing an important source of energy and nutrients that support other organisms in the food web (e.g., zooplankton and herbivorous fish). However, persistently high levels of algae in Lake Tahoe are considered undesirable. Phosphorus occurs naturally in the soils of the Lake Tahoe Basin, and is delivered to surface waters and Lake Tahoe through soil erosion and subsequent transport in streams and storm water, atmospheric deposition, and fertilizer runoff (Lahontan & NDEP, 2010a). The Lake Tahoe Total Maximum Daily Load (TMDL) estimated that a 46 percent reduction (from 2004 loading estimate) in total phosphorus load from urban upland sources over 65 years would be required to achieve the pelagic clarity standard.

Human and Environmental Drivers

Landscape modification (e.g. impervious cover such as roads or residential and commercial development or logging) influences the volume of runoff, erosion rates, and the ability of the watershed to retain sediment and nutrients. Sediment and nutrient load in stormwater runoff is influenced by the type, magnitude, and location of landscape modifications and the extent to which practices to mitigate potential impacts (e.g. water quality BMPs) are in place. A variety of natural factors also influence the load of sediment and nutrients in stormwater including climate, weather, landscape topography, and vegetation. The TMDL estimated that 26 percent of total phosphorus load originates from urban upland sources.


Management with Numeric

Reduce total annual nutrient and suspended sediment loads as necessary to achieve loading thresholds for tributaries and littoral and pelagic Lake Tahoe.

Reduce loads of fine sediment particles, total nitrogen, and total phosphorus as established by Lake Tahoe TMDL

Indicator Status, Trend, and Confidence
View Evaluation Legend
Status: Insufficient Data to Determine Status or No Target Established
Trend: Insufficient Data to Determine Trend
Confidence: Low

Status, Trend, and Confidence Details


Insufficient data to determine status. Data reported in this assessment is load as measured at specific catchments and no overall estimate of load was available at this time. Load reduction estimates and condition assessment commitments are documented in the credit accounting platform of the TMDL. A more robust picture of load in stormwater will be available in March 2017 after credit declaration and associated verification associated with the first TMDL milestone is complete. In sites that monitored in both the 2014 and 2015 water years total phosphorous load was 24.5 kilograms in 2014 and 13.7 kilograms in 2015. Three additional sites were added in water year 2015 and total monitored load was 33.2 kilograms in water year 2015. The two years are not comparable because three additional sites were added in 2015 and total surface volume was much greater in 2014.


Insufficient data to determine trend. The first Region wide load reduction estimates are expected in March 2017. These estimates will serve as the basis for evaluating trend in future evaluations.


Status: Low. Where insufficient data exists to determine status, confidence in the status determination is low. There is moderate confidence in the data because it is collected using widely recognized, standardized national protocols (see monitoring approach) with quality assurance/quality control procedures. Only a small proportion of the outflows are sampled and not all runoff events are sampled. Regional estimates of overall load and load reduction are not available at this time.

Trend: Low. No trend assessment was performed because both the nature and limited duration of the data preclude trend assessment. v

Overall: Low.


Implementation and Effectiveness
Programs and Actions Implemented to Improve Conditions

The TRPA Regional Plan requires the use of best management practices (BMPs) for new residential and commercial development, and BMP retrofit regulations for developed properties. For example, section 60.4.6.A.1 of TRPA Code of Ordinances requires properties be able to infiltrate the 20-year, one-hour storm into groundwater. The Regional Plan is also designed to limit growth and shift development from sensitive to less sensitive lands. All of these requirements contribute to reducing fine sediment and nutrient runoff from developed areas. The Regional Transportation Plan complements these by encouraging use of public transit and alternative transportation modes, and reducing reliance on private automobile. Water quality mitigation fees, collected on projects that create new cover, support erosion and storm water pollution control projects. Projects completed by EIP partners since between 2009 and 2015 have:

• Issued 18,076 BMP certificates to developed commercial, multifamily and single family residential properties.
• TRPA’s grant funded Stormwater Management Program focuses compliance and maintenance verification activities on priority commercial and large multi-family residential properties in coordination with local jurisdictions. In 2015, Stormwater Management Program staff notified 2,441 parcel owners with BMP Certificates issued more than five years ago that maintenance was due and re-issued 186 BMP Certificates following maintenance verification.
• Completed street sweeping on 24,644 miles of roads.
• Retrofitted 120.55 miles of road and decommissioned an additional 7.4 miles of road.

The Stormwater Management Program leads annual BMP trainings for contractors, local jurisdictions and real estate professionals. The Stormwater Management Program also authors articles in “Tahoe In-Depth”, and participates in a variety of public workshops and events to increase BMP awareness and promote proper design, installation and maintenance. Public outreach and educational campaigns (such as the “Take Care” campaign) highlight for residents and visitors what they can do maintain a healthy environment. Between 2012 and 2015 the South Tahoe Environmental Education Coalition delivered 36 educational programs and reached nearly 30,000 individuals.

TMDL Management System Handbook guides the actions of agencies in the Region to reduce inputs of nutrients and sediments into Lake Tahoe (Lahontan and NDEP, 2014). As part of the TMDL each jurisdiction in the Region prepares a load reduction plan (pollutant load reduction plans in California and stormwater load reduction plans in Nevada) that detail the steps to achieve the specified load reductions. The Lake Tahoe TMDL estimated that a 10 percent reduction in total phosphorous load from urban sources would be required to achieve lake clarity standards (Lahontan and NDEP, 2010b).

Effectiveness of Programs and Actions

Each year the actions of the TMDL implementation partners are summarized and evaluated in the TMDL Performance Report. The pollutant tracking system for urban stormwater was being refined during the reporting period. Future evaluations will use the estimated reductions in urban source pollutants to assess the effectiveness of programs and actions implemented to reduce pollutant load from urban sources (Larsen and Kuchnicki, 2015a).

TRPA infiltration requirements were designed to strike a balance between environmental benefit and cost. A 2011 synthesis of existing knowledge found diminishing returns from increasing storm retention capacity beyond the 20-year, one-hour storm. The synthesize found that doubling retention capacity required to handle the 20-year, one-hour storm would only increase annual retention by seven percent (2ndNature and NHC, 2011). TRPA Code Section 60.4.6.A.1 further requires a one-foot separation between seasonal high groundwater and the bottom of an infiltration system to protect groundwater resources.

In the long term, partners will be able to measure overall load reductions from surface runoff. However, with currently available data, the primary way to measure the effectiveness of programs and actions is to assess the effectiveness of BMP’s at reducing sediment and nutrient loads. The currently available data enables the assessment of the effectiveness of individual BMP’s in reducing sediment and nutrient loads. The following results on the effectiveness of BMP’s were reported in the 2014-2015 Stormwater Monitoring Report (Tahoe Resource Conservation District, 2015):

• Selected BMP catchment basins (Pasadena, Rubicon, SR 431 Contech, SR 431 Jellyfish) decreased total phosphorus load by 30 percent in water year 2014 and 23 percent in water year 2015

Further analysis of program effectiveness, may be possible by looking at response of secondary indictors (e.g. suspended sediment in tributaries and lake clarity) that are the subject of the standards.

Interim Target

Insufficient data is available to set an interim target at this time.

Target Attainment Date

Insufficient data is available to set a target attainment date.

Analytic Approach

The Lake Tahoe TMDL requires urban jurisdictions to report pollutant load estimates using the Lake Clarity Crediting Program and associated tools. The pollutant load reduction model (PLRM) provides a consistent method for evaluating both baseline and expected conditions associated with pollutant load reduction actions. The model provides estimates for the expected benefits of actions and on-the-ground field verification methods confirm treatment facility and roadway conditions are consistent with modelled parameters. Load reduction estimates and condition assessment commitments are documented in the credit accounting platform. Credit declaration and associated verification to document the first TMDL milestone is expected in March 2017. The raw RSWMP data detailed in this assessment will be used to help calibrate stormwater treatment BMP performance assumptions in PLRM. RSWMP sites will also provide data to aid in verifying the PLRM estimated changes in load are consistent with observed changes.

Monitoring Approach

No changes recommended

Modification of the Threshold Standard or Indicator

Objective determination of “attainment” status for standards without a specific target is a recurrent challenge both in the Region and in the larger field of monitoring and evaluation (M&E). The standard should be assessed against best practice for the establishment of standards and indicators for M&E, and amended as necessary to improve the evaluability of the standard and the information it provides for management. Development of any new standards should also consider the benefits of alignment with the standards and management strategies implemented through the Lake Tahoe TMDL program. The Lake Tahoe TMDL estimated that a 46 percent reduction in total phosphorus load, from 18 Metric Tonnes per year (MT/yr) to 9.72 MT/yr, from urban sources would be required to achieve lake clarity standards (Lahontan and NDEP, 2010b). Standard revision should also consider simplification of the text of the existing standards to ensure that the desired outcomes are readily apparent to most readers. The construction of the current standard, which references load reduction “as necessary to achieve loading thresholds for tributaries and littoral and pelagic lake Tahoe” as the target for the standard is confusing and requires readers to look up other standards to understand the standard’s objective.

Attain or Maintain Threshold

No changes recommended. The 2015 Findings & Program Recommendation Memo for the TMDL reported that no new findings relative to urban stormwater were reported in previous calendar year (Larsen and Kuchnicki, 2015b).


Map shows all stormwater monitoring locations during water years 2014 and 2015. Source: Tahoe Resource Conservation District

Additional Figures

No figures available.

Historic 2011 Threshold Evaluation
View Evaluation Legend

Status Insufficient Data to Determine Status or No Target Established
Trend Insufficient Data to Determine Trend
Confidence Low

The 2011 Evaluation Report has not yet be uploaded or is unavailable.