To All Who Share Our Commitment to Lake Tahoe,

It is my pleasure to present the draft 2023 Threshold Evaluation Report. This draft report represents the combined work, knowledge, and expertise of many individuals and organizations committed to the protection and restoration of Lake Tahoe. On behalf of the Tahoe Regional Planning Agency (TRPA), we thank you all for your contribution to this comprehensive report.

New findings on Lake Tahoe’s geologic history provide a broader perspective on this work. Recent research shows that Lake Tahoe first took shape more than 2.3 million years ago, making it the oldest lake in North America and the third oldest waterbody in the world. We also recognize the importance of the native Washoe people whose spiritual connection to Lake Tahoe has stood for 10,000 years.

Today, the region is reconciling environmental impacts that began just 150 years ago, a small fraction of the lake’s true history. Meanwhile, regional collaboration to protect the lake began just 55 years ago with the signing of the unique interstate compact between Nevada and California that created this agency. Rather than diminishing our work, this knowledge makes our founding principles of conservation and community vitality all the more important.

The significance of each step forward is evident in the draft report. During the 2020-2023 reporting period, TRPA and basin partners surpassed a landmark goal to restore or enhance 1,100 acres of Lake Tahoe’s most sensitive land—Stream Environment Zone. Pursued for more than 40 years, this accomplishment wouldn’t have been possible without the first acre or the last and the collaborative partnership that makes up the Environmental Improvement Program.

Over the coming months, TRPA staff will be collecting public and partner input on the draft and expect to present a final report to the Governing Board in June of this year. The complete report will include recommended actions in response to the findings, changing conditions, and advancements in science.

We look forward to working with all stakeholders to continue to protect and restore this spectacular place for generations to come.

Sincerely,

Julie W. Regan
Executive Director

Key Takeaways:

Lake Tahoe is one of the most spectacular mountain lakes in the world with environmental protections to match. The states of Nevada and California created the Tahoe Regional Planning Agency (TRPA) in 1969 to develop a Regional Plan to better manage development practices and protect the region’s pristine environment for future generations.

In 1982, the agency established comprehensive, science-based environmental goals for the region, called thresholds. The agency issues a threshold evaluation report every four years to assess the status of each threshold and to monitor regional progress toward achieving the adopted standards. The 2023 Threshold Evaluation is the region’s eighth evaluation and provides a comprehensive overview of Lake Tahoe’s environmental health as indicated by the 140 current threshold standards. To ensure the technical rigor of the evaluation, the independent Tahoe Science Advisory Council led a peer review of the report.

While the evaluation focuses on specific standards in the ten threshold categories, several overarching themes are present throughout the evaluation that are essential to understanding the environmental trends in the basin. This executive summary includes a brief history, analysis of certain crosscutting events, collective progress, and emerging trends and ongoing challenges that stand out during this threshold evaluation period of 2020 to 2023. 

DaɁaw (Lake Tahoe) is the homeland of the waší∙šiw (Washoe people – the people from here). The Washoe are the aboriginal stewards of the land in and around the Lake Tahoe Basin and are federally recognized as the Washoe Tribe of Nevada and California. For the Tribe and their descendants, Lake Tahoe is the center of the world both geographically and spiritually.  

In the 1960s, Lake Tahoe faced a critical crossroads as its fragile ecosystems had degraded from a century of logging, agricultural practices, and auto-centric development. Wetlands were filled for housing, hotels, and businesses, and the increased pollutant load caused the lake's renowned clarity to plummet at a rate of 1.2 feet per year.

In 1987, TRPA adopted a Regional Plan that outlined actions to achieve the thresholds.  The plan established overall caps on development, set an urban boundary, prevented future subdivisions, and prohibited new development on Tahoe’s most sensitive lands. During the same period, the two states and the federal government prioritized public land acquisitions to reduce future development and preserve open space in the watershed. Soon federally managed lands increased to more than 75 percent of the region. Between 1981 and 1997 the rate of Lake Tahoe clarity loss slowed to 0.7 feet per year.

While this landmark plan and regulatory actions put the basin on a trajectory towards threshold attainment, the effects of past environmental degradation were far-reaching. In the 1990s, scientists sounded the alarm that more would need to be done to restore the environmental degradation of the past. In 1997, at the first Lake Tahoe Summit, President Bill Clinton signed an executive order to establish the Lake Tahoe Environmental Improvement Program, or EIP.

The EIP is a collaborative capital investment program to accelerate threshold attainment. More than 80 entities across the region are working together to implement public and privately funded projects that improve environmental conditions and provide lasting community benefits. The Lake Tahoe Restoration Act reauthorization in late 2016 enabled EIP partners to continue critical project work. This influx of federal funding catalyzed other federal, state, local, and private contributions for strategic implementation of some of the highest-priority and largest projects within the EIP.

Through the combination of regional development standards and EIP projects, the 2023 Threshold Evaluation shows nearly three times as many thresholds improving than declining. 

In 2021, more than 1.5 million acres burned across the Sierra Nevada, including the Dixie and Tamarack fires in neighboring counties. These fires sent heavy smoke into Tahoe, darkening the skies and creating unhealthy air pollution levels, with ash falling across the local environment. The 2023 Threshold Evaluation Air Quality section highlights the contrast between the generally good and improving annual air quality, and how wildfire smoke caused exceedances and downward trends in standards for single-day and shorter periods.

The Caldor Fire started on August 14, 2021, and burned for 68 days, ultimately becoming the second fire in recorded history to jump the crest of the Sierra Nevada. The last major fire in the Tahoe Basin was the 2007 Angora Wildfire, which burned 3,100 acres in the southern portion of the watershed. The Angora Fire destroyed approximately 250 homes and led to changes in policy, improved coordination, and stronger partnerships, including the creation of the Tahoe Fire and Fuels Team. By comparison, the Caldor Fire burned 221,800 acres, including 10,000 acres within the Lake Tahoe Basin and destroyed more than 1,000 homes outside the region. Thanks to the efforts of firefighters and key fuel reduction projects completed by Tahoe Fire and Fuels Team partners, not a single primary residence in the Tahoe Basin was lost.

The Caldor Fire showed that the hazardous fuel reduction treatments completed over the past 20 years as part of the EIP were successful in slowing fire activity, allowing firefighters to safely battle the blaze and prevent catastrophic losses in those areas. TRPA’s recent code changes will extend these benefits to hard-to-reach areas by allowing mechanical thinning on slopes up to 50 percent gradient, using modern equipment that prevents erosion and maintains slope stability.

The Caldor Fire exemplified the dual role of fire in the Tahoe Basin, acting as both a natural restorative force and, depending on fire severity, a potential driver of ecosystem damage. Within the Tahoe Basin, 3,750 acres burned in the Caldor Fire at low or moderate severity, which aided biodiversity and enhanced resilience to emerging threats. In contrast, the 6,170 acres that burned at high or very high severity led to destructive outcomes, including habitat loss, soil degradation, increased erosion, and major recovery challenges for the affected landscapes.

Longer wildfire seasons, and more intense fires in the Sierra Nevada threaten the safety of communities and the health of the ecosystem. Partners continue to work to prepare the region for the next fire, conducting defensible space inspections to ensure properties meet wildland-urban interface (WUI) standards, implementing prescribed fire treatments to reduce hazardous fuel loads, and utility corridor vegetation management to reduce ignition sources and protect critical infrastructure. The successful evacuation of 30,000 South Shore residents during the Caldor Fire also provided lessons learned to regional fire chiefs and emergency management agencies as they begin coordinating evacuation plans in the basin for the first time. These efforts remain essential to the region’s fire preparedness.

Protecting and restoring meadows and wetlands has long been a key priority for TRPA and EIP partners in the watershed, and the 2023 Threshold Evaluation includes a significant milestone. In 1982, the region set a threshold target of restoring 25 percent of disturbed, developed, or subdivided stream environment zones (SEZs), which are wetlands. Controls set more than 40 years ago by the Regional Plan have prohibited further disturbance of SEZ, which has prevented any backsliding. To accomplish the restoration goal, EIP partners have completed hundreds of restoration projects and property acquisitions. Today, more than 1,100 acres of previously disturbed SEZs have been restored, which not only attained, but surpassed the 1982 threshold standard.

As the partnership began approaching attainment of the standard, TRPA’s Governing Board adopted a new threshold standard focused on improving the overall condition of SEZs, rather than solely on the acreage of restoration. While the new SEZ standard is evaluated in the 2023 Threshold Evaluation, it is important to recognize the shared success of meeting a landmark restoration target set in the early 1980s. The new SEZ standard continues this restoration work while strengthening ongoing and future restoration projects.

Outdoor recreation and visitation patterns have been changing in the Tahoe Region for decades, and the COVID-19 pandemic compounded and accelerated these trends. The legalization of Tribal gaming in California and the rise in online gaming began eroding the draw of Tahoe as a gaming destination in the early 2000s. Over that same time, the popularity of outdoor recreation increased here and across the nation. Advances in mobile phone and global positioning system (GPS) technology and extensive growth of social media also began drawing people to different places, further altering visitation patterns in the region. While overall traffic counts and population have remained stable, shifts in the volume of visitation to different areas have strained aging infrastructure and Tahoe’s transportation system.

A new collaboration of land managers, business owners, public agencies, and nonprofits from across the Tahoe and Truckee region recently formed the Destination Stewardship Council to address outdoor recreation issues that reached a fever pitch during the COVID-19 pandemic. This collaborative group conducted extensive public engagement to create a shared vision in the Lake Tahoe Destination Stewardship Plan. This plan outlines new approaches and research tools to better manage Tahoe’s tourism and outdoor recreation sector, with links to multiple TRPA threshold categories.

The current threshold standards for recreation are policy statements that seek to ensure the quality and availability of recreational opportunities to the public. In the coming years, TRPA and partners will work with the Destination Stewardship Council to adopt new, measurable goals for the recreation threshold reflecting the actions outlined in the Destination Stewardship Plan. Corridor management plans have been adopted for portions of state highways along Tahoe’s East, West, and North Shores that serve as access routes to popular beaches, sightseeing, and outdoor recreation areas. These plans create a central vision for each transportation corridor. Prioritizing corridor projects will shift the way people arrive to their recreation destinations from being auto-dependent to more transit and multi-modal focused. 

The TRPA Shoreline Plan adopted in 2018 includes measures to increase safety, improve the recreation experience, and curb boat noise along Tahoe’s iconic shoreline. TRPA launched the Tahoe Boating App to help boaters navigate the new shorezone ordinances with an interactive map showing their location in relation to no wake zones. The app also alerts users to new protocols to prevent the spread of aquatic invasive species in the lake including New Zealand mudsnails. More than 17,000 users downloaded the boating app between 2019 and 2023.

TRPA has continued to update and strengthen thresholds as scientific understanding of Lake Tahoe’s unique ecosystem grows and new threats emerge. The 2023 Threshold Evaluation includes a report on new Aquatic Invasive Species (AIS) control standards. The new standards set ambitious targets for control of aquatic invasive plants, in particular. The pace and scale of AIS control projects have significantly increased to meet the challenge (Figure 1). The Tahoe Keys Control Management Test began in summer 2022 to find the best combination of methods to treat large-scale weed infestations to protect native habitat and water quality in the lake.  

Ultraviolet light, EPA-certified aquatic herbicides, bottom barriers, diver-assisted plant removal, and laminar flow aeration were tested across 41.5 acres in the lagoons of the Tahoe Keys, the largest and most persistent population of aquatic weeds and the highest priority area for AIS control in the region. The test returned a wealth of information and will be analyzed by the Tahoe Science Advisory Council to inform long-term solutions.  

A setback occurred in the form of a new invader, the New Zealand mudsnail, found by divers in 2023 in areas of the South Shore. The discovery was the first new aquatic invasive species detected in Lake Tahoe since the inception of the Tahoe Watercraft Inspection Program more than 15 years ago. In 2008, TRPA and Tahoe Resource Conservation District created the Lake Tahoe Watercraft Inspection Program and have since inspected more than 117,000 vessels prior to launching to prevent new AIS from entering Lake Tahoe, Fallen Leaf, and Echo lakes.

Following rapid response protocols, TRPA, Tahoe Resource Conservation District, and California Department of Fish and Wildlife engaged the Tahoe Science Advisory Council to convene a group of experts to guide the response. TRPA and the Tahoe Resource Conservation District deployed lake-wide surveys and stream eDNA (environmental DNA) sampling while immediately strengthening protocols for boats entering and exiting the lake and non-motorized watercraft such as kayaks and paddleboards. Preventing new AIS from entering lakes in the Tahoe Region is a key threshold standard and is one of the primary goals of the EIP. The discovery pushed the AIS prevention threshold standard out of attainment for the first time since its adoption in 2012.

The 2023 Threshold Evaluation is the first to report on the Transportation and Sustainable Communities threshold category adopted in 2021. A key element of transportation improvements in the Lake Tahoe Region are strategies to deliver more projects at a faster pace. Recent increases in transportation funding are helping move the region’s transportation vision forward. The 2023 evaluation shows that new Transportation threshold standards for vehicle miles traveled (VMT) and per capita VMT both declined.

In 2022, the Bi-State Consultation on Transportation for Lake Tahoe, led by Nevada Department of Conservation and Natural Resources and the California Natural Resources Agency, established the “7-7-7” transportation funding framework. The agreement is a multi-sector funding strategy to raise approximately $20 million annually to fund high-priority, regionally significant transportation projects that will improve transit connectivity and reduce VMT across the region. Over the last two years, the partnership has exceeded that annual target and raised more than $50 million in new revenues. These funds are in addition to the revenue forecasted in the 2020 Regional Transportation Plan and Sustainable Communities Strategy, placing the region ahead of the forecasted funding to implement the projects in the plan. In the 2023/2024 fiscal year, local operating funding for transit rose to nearly $8.5 million per year, the highest ever seen in the Tahoe Basin.

Despite the recent funding increases, the gap to fully fund the Regional Transportation Plan is still significant and additional work remains to achieve the region’s bold transportation vision.

The 2023 Threshold Evaluation also highlights numerous remaining and emerging challenges. Chief among these concerns is the impact that extreme weather, rising temperatures, and ecological changes are having on the clarity of Lake Tahoe. Fifteen years ago, Lake Tahoe water quality agencies established the Lake Tahoe Total Maximum Daily Load as the science-based framework to restore the historic clarity of the lake. Partners have worked diligently to reduce pollutant loads and continue to meet increasingly aggressive targets. While annual average clarity has stabilized from its earlier decline and clarity during winter months is improving, summer clarity is worsening. Recent data (Figure 2) from the University of California, Davis Tahoe Environmental Research Center show a divergence between summer and winter clarity in the lake. The winter trend implies that restoration and stormwater treatment projects are having the desired effect. Declining summer clarity suggests other factors are influencing seasonal conditions. The Tahoe Science Advisory Council and water quality partners are actively working to better understand the causes of these variations and identify management strategies to improve water quality.

Every four years the Threshold Evaluation is compiled using the best available science and data from a wide range of partners to assess progress towards the region’s shared goals. This evaluation brings together years of monitoring data from federal, state, and local agencies, research institutions, and community organizations, whose contributions are essential to tracking progress and informing policy decisions. We are deeply grateful for the dedication of these partners, whose collaboration ensures that our environmental thresholds remain a strong foundation for protecting and restoring the Lake Tahoe Region for generations to come.

This Threshold Evaluation considers environmental conditions relative to 140 standards across 10 threshold categories. To determine the status, a threshold standard must be clear and measurable, have an established target, and monitoring data must be accessible. Status determinations were made for 112 (80 percent) of the standards. Of these 112 standards, 88 (79 percent) were found to be either “at or better than target” or “considerably better than target” or are management standards or policy statements that have been achieved by their adoption into the Regional Plan. Of the 28 standards where no status determination was possible, 13 do have an established target, and 15 did not have sufficient data.  

Figure 1 summarizes the threshold status results, with an individual icon for each indicator of the ten threshold categories. Standards were placed into one of three categories: Attainment (green) – where conditions are at or better than the standard, or where policy-related standards have been implemented; Non-attainment (orange) – where conditions are worse than the standard; and No Status determination (gray) - where ambiguity in the standard, lack of an established target, an unknown historic baseline, or insufficient data precluded a status determination. Most of the threshold standards without status determinations are in the water quality and noise sections, largely due to ambiguity or obsolescence of the original standard. Newly adopted thresholds are indicated with a “#” sign, and thresholds where the status changed from the 2019 to the 2023 evaluation are indicated with an asterisk (Ö).

Figure 1: Summary of 2023 Threshold Standard Status by Threshold Category 

Tahoe Regional Planning Agency (TRPA) staff and partner organizations incorporate the latest science and best practices into the threshold standards and their evaluation. With input and support from the Tahoe Science Advisory Council (Science Council) and Environmental Improvement Program (EIP) partners the agency updated thirteen threshold standards last year. The modifications applied new science to the standard for Tahoe yellow cress, adopted specific and measurable targets for aquatic invasive species (AIS) control, and established an ambitious new target for wetland and meadow restoration, also known as Stream Environment Zones (SEZs). 

To determine the trend or direction a threshold standard is moving, the standard must be clear and measurable, and monitoring and data must be accessible for a sufficient number of periods to be able to assess the trend. Trends indicate whether the data show that the conditions are improving, stable with little or no change, or declining. Numerous threshold standards call for the non-degradation of environmental conditions or require a specific value to be maintained. Often the goal for these standards is to be stable or have little to no change.  

For the 2023 Threshold Evaluation, trend determinations were possible for 78 standards evaluated. Where a trend could be assessed, the vast majority are either improving or show little or no change. Improving trends outnumbered declining trends nearly three to one. Conditions were declining for six standards, while 55 showed little or no change and 17 standards were improving. Of the 140 standards, 29 are policy statements or management standards, all of which have been achieved by their adoption or implementation through the Lake Tahoe Regional Plan or TRPA Code of Ordinances.

·        Annual average results continue the long-term improvements in Air Quality.

·        Wildfires and extreme events are impacting single-day and short-term standards.

Clean air, free from pollutants like carbon monoxide, ozone, and particulate matter, is essential for human health, social well-being, the environment, and the economy.  Lake Tahoe Region partners preserve and protect the basin’s air quality in a number of ways including limiting development, restoring forests, and improving transportation systems to reduce emissions. There are thirteen adopted Air Quality standards. Eleven are in attainment, one is non-attainment, and one management standard was previously achieved by its adoption into the Regional Plan. The Worst Regional Visibility Days standard dropped out of attainment from the prior evaluation due to smoke from wildfires. 

Ambient air quality conditions in the Lake Tahoe Region continue to trend toward long-term improvement. However, the increased frequency and intensity of wildfires show a dramatic change in single-day air quality indicators. The emerging pattern is that air quality in the region meets the highest daily concentration standards in years without significant wildfire activity but exceeds these standards when wildfires are prevalent in and around the Tahoe Basin. This pattern was most notable during the summer of 2021 when the basin was affected by the Caldor, Tamarack, and Dixie fires. A similar pattern is observed in the regional visibility indicator for Worst Visibility Days, which shows an increase during years with high levels of unhealthy smoke in the region. 

Inside and outside of the region, overstocked forests, extreme weather, rising temperatures, and changes in precipitation will likely lead to more frequent and intense wildfires. Regardless of continuous reductions in vehicle emissions and other particulate sources, wildfires could result in more frequent exceedances of single-day air quality threshold standards.  Forest restoration  through hazardous fuels reduction and using prescribed fire to return the natural fire cycle remain top EIP priorities to address these threats.

·        Regional protections have stabilized the loss of Lake Tahoe’s clarity, but major swings between winter and summer clarity must be researched.

·        The discovery of New Zealand mudsnail and new, aggressive targets for aquatic invasive plants will require continued work.

Lake Tahoe is designated an Outstanding National Resource Water under the federal Clean Water Act, requiring an anti-degradation policy, the highest level of protection. Strict water quality standards adopted by TRPA and state agencies are essential for safeguarding public health, protecting the environment, supporting the local economy, and ensuring the sustainable use of water resources.  There are 37 Water Quality standards. Of those, seven are in attainment, 10 are management standards previously achieved by their adoption into the Regional Plan, and six are in non-attainment. The status of 14 water quality standards could not be determined due to insufficient monitoring information or the lack of an established target. Of the six standards not in attainment, two are new goals for aquatic invasive weeds adopted in 2024 that were not expected to be in attainment.

Tahoe’s famed lake clarity has awed visitors and residents for generations and is a high-profile measure of the natural function of the watershed. The Lake Tahoe Regional Plan protected lands that are essential to lake clarity, however between the late 1960s and 1990s, the lake’s average annual clarity declined by nearly a foot a year.

In 2011, after extensive research with water quality experts on what was causing clarity loss and strategies to address it, the states of California and Nevada adopted the Lake Tahoe Total Maximum Daily Load strategy, or TMDL. The TMDL charted a 65-year course to reduce pollutants entering the lake in order to restore the lake’s historic level of clarity. TRPA and water quality partners adopted the Clarity Challenge as a commitment to implement the TMDL and return Lake Tahoe’s annual average clarity to nearly 100 feet.

Today, TMDL implementers (CalTrans, Nevada Department of Transportation, City of South Lake Tahoe, Douglas County, El Dorado County, Placer County, and Washoe County) are collectively preventing 500,000 to 600,000 pounds of fine sediments from reaching the lake every year. As a result of pollutant load reductions, restoring stream environment zones, and removing development from sensitive areas, the decline of lake clarity has stabilized.

However, managing stormwater and restoring streams and wetlands may not be the only keys to restoring lake clarity. While clarity in winter months is improving and the lake’s average clarity has stabilized, clarity during Tahoe’s increasingly hot summer months continues to decline. Scientists and managers are evaluating long-term trends and gathering new information to better understand the role of increasing temperatures and biological/ecological processes on the health of the lake and to develop management strategies to continue progress on lake clarity. 

Aquatic invasive species (AIS) continue to be a major focus of the EIP, and the region celebrated both accomplishments and setbacks during the four-year reporting period. The control program continues to increase the size and scale of treatments in the region. In 2023, divers treated over 100 acres of aquatic invasive weeds in Lake Tahoe, including sites like Emerald Bay and the Taylor Tallac marsh and creek ecosystem. The Tahoe Keys Property Owners Association completed the third year of the Control Methods Test in the lagoons of the Tahoe Keys. The Tahoe Key lagoons harbor the largest and most persistent population of aquatic weeds growing in the region, infesting over 172 acres of waterways, more than eight times all other infestations combined. Data from the test will inform a long-term management plan for the Keys aquatic weed infestation.

A setback occurred with the detection of a new aquatic invader, New Zealand mudsnails, in 2023 off the South Shore of Lake Tahoe. It was the first time since the inception of the Lake Tahoe Watercraft Inspection Program in 2008 that a new aquatic invasive species has been discovered in Lake Tahoe. Preventing new AIS from entering Lake Tahoe is one of the primary goals of the EIP and a Water Quality threshold standard. New AIS management protocols are now in place to contain the new invasion to the extent possible and showed positive results outside of the reporting period. 

·        Landmark stream zone restoration target achieved, strengthened with new long-term target.

·        Regional Plan protections and removal of legacy development from sensitive areas showing progress.

Soil conservation measures are vital for ensuring the health of the land and vegetation, protecting natural filtration, and preventing runoff into the lake. There are 11 Soil Conservation standards, seven are in attainment, one management standard was previously achieved by its adoption into the Regional Plan, and three are in non-attainment.

Since adoption of the 1987 Regional Plan, TRPA policies have prohibited new development and impervious coverage such as buildings and pavement in Lake Tahoe’s most sensitive (Class 1b) soils. A major goal of the EIP is to remove legacy development from these Stream Environment Zones (SEZs) and the 2012 Regional Plan created incentives that allow private property owners to help increase the pace of restoration.

Following decades of restoration projects and property acquisitions, today more than 1,100 acres of previously disturbed SEZ have been restored by partners, which attained the threshold standard first set in 1982.  TRPA has directed millions in mitigation funds to SEZ restoration projects and has implemented recommendations from past threshold evaluations to convene science and restoration partners  to strengthen  SEZ standards.  

TRPA adopted a new SEZ standard in April 2024 that focuses less on acreage and more on the quality of SEZ function. The 2023 Threshold Evaluation is reviewing that standard for the first time using data collected through 2023. While it is important to appreciate the landmark achievement of 1,100 acres of SEZ restoration, this threshold evaluation also sets a course for the long-term restoration of disturbed wetlands that ensures projects regain the historic function and value of these critical lands. 

·        Over 92 percent of survey respondents said outdoor experiences at Lake Tahoe were enjoyable.

·        Changes in visitation are being managed through the first-ever Lake Tahoe Destination Stewardship Plan.

Recreation standards ensure that recreational activities are sustainable, safe, and enjoyable for all, while also protecting the environment and supporting community well-being. These standards balance the needs and desires of people with the preservation of natural resources, public safety, and equitable access. The two adopted Recreation standards have both been achieved. Each are statements of policy and not numerical standards. These standards ensure recreational opportunities keep pace with public demand, recreational facilities are prioritized, and the quality of the outdoor recreation experience is maintained. 

Over the last 20 years, the Tahoe Region has experienced a significant shift in recreation demand and the pattern of visitation. At the same time demand for outdoor recreation has grown across the nation, changes in the gaming industry have shifted some of Lake Tahoe’s visitation from resorts and town centers to popular recreation areas and sightseeing corridors.

Limited data has been collected about recreational behavior in the Lake Tahoe Region and what has been collected is site specific rather than basin wide. In 2023, TRPA and partners engaged the Tahoe Science Advisory Council to review best practices in monitoring outdoor recreation access and quality to better assess the state, quality, and trends in recreation at Lake Tahoe. TRPA is currently evaluating the Council Report and recommendations that may inform a future update to the recreation thresholds to better address today’s challenges and desired conditions

The changes evident in regional visitation have come with new impacts to public safety, environmental quality, and quality of life for residents. In 2022, seventeen partner organizations including TRPA, public land managers, and destination management organizations participated in a community-driven process to create the first Destination Stewardship Plan for Lake Tahoe Region, including Truckee. The plan creates a shared vision where people, communities, and nature benefit from a thriving tourism and outdoor recreation economy. In 2023, these organizations signed an agreement to form the Destination Stewardship Council to set the plan into action. 

·        Caldor Fire and impacts from drought and insects are increasing regional tree mortality.

·        Hazardous fuels reduction and forest initiatives are leading to a more resilient and healthy forest.

Healthy plant life is fundamental to the overall function of ecosystems. A vibrant plant community also supports other thresholds, such as wildlife biodiversity, water quality, and soil health. There are 22 adopted Vegetation Preservation standards, nine are in attainment, five are management standards previously achieved by their adoption into the Regional Plan, and eight are in non-attainment. 

In addition to the impacts from the Caldor Fire described in the Executive Summary, vegetation in the Tahoe Region is recovering from the impacts of historic land management. Lake Tahoe’s forests were largely clear-cutting during the Comstock era. As the forest rebounded, a national policy of fire suppression replaced natural fire regimes and cultural burning practices of the native Washoe people that kept Lake Tahoe’s forests healthy and less prone to catastrophic wildfire.

More than a century later, tree density in the region is well above historic levels, leading to less availability of ground water, increased tree mortality, and heightened wildfire risk. In 2023, an estimated 1.7 million trees died within the Lake Tahoe Basin, primarily due to drought conditions that limited the ability of trees to defend themselves against bark beetles. Mortality was highest amongst the white and California red fir stands along the West Shore.  

For more than 20 years, regional partners comprising the Tahoe Fire and Fuels Team have been actively engaged in reducing hazardous fuels and implementing forest health initiatives, particularly within the wildland-urban interface. To date, these efforts have resulted in the treatment of more than 94,000 acres of forest, aimed at reducing hazardous fuels and enhancing ecosystem resilience and community wildfire protection. In this threshold evaluation period, 14,000 acres of treatment were completed basin wide. A notable example of this collaborative effort is the partnership between Liberty Utilities, NV Energy, the USDA Forest Service, and local fire districts. Together, they treated more than 1,000 acres of forest along powerline corridors during the evaluation period with more work underway. By thinning wider areas, these projects create defensible space around critical utility infrastructure, reduce wildfire risk, and improve overall forest health.  

Additionally, Tahoe yellow cress (TYC) continues to be an ongoing conservation success story in the region. This special plant species grows in sandy beach areas and is endemic to Lake Tahoe, which means it is found nowhere else in the world. Habitat protection by public land managers have been matched by TRPA permit requirements for shoreline property owners to preserve populations and protect habitat have increased TYC populations in the basin.

In 2024, TRPA and conservation partners updated the TYC threshold standard to reflect the relationship between Lake Tahoe’s water level and occupied population sites. Lower lake levels expose more habitat and result in a greater number of sites being occupied. As Lake Tahoe rises, the amount of available habitat declines along with the expected number of TYC-occupied sites. This new standard accounts for these fluctuations and TYC populations met the new threshold standard for the 2023 evaluation.  

·        Vehicle miles travelled (VMT) and VMT per capita declined with visitation shifts, record wildfires, and the COVID-19 pandemic.

·        Further measurement is needed to tell if reductions are short lived or an ongoing trend.

Transportation is a major contributor to greenhouse gas emissions, especially from cars, trucks, and other motor vehicles. Sustainable transportation policies, such as those promoting biking, walking, electric vehicles, fuel efficiency, and public transit, can reduce carbon emissions by reducing reliance on the private automobile, thereby reducing air pollution and energy consumption. In April 2021, TRPA adopted the Transportation and Sustainable Communities threshold category that included a single standard—vehicle miles traveled (VMT) per capita. The new standard is in attainment for the 2023 Threshold Evaluation. 

The Transportation and Sustainable Communities threshold standard is designed to reduce reliance on the automobile, improve mobility options, and support attainment of greenhouse gas emission reduction goals of California and Nevada. TRPA’s unique planning authority allows it to closely coordinate land use through the Regional Plan and transportation through the Regional Transportation Plan. The two plans work together to promote compact, mixed-use, and vibrant town centers, that are safe, walkable, bikeable, and served by transit. 

The COVID-19 pandemic disrupted travel patterns to, from, and within the Tahoe Region. The impacts of those disruptions are evident in the latest transportation data from the states of Nevada and California, which indicate that the three-year average VMT in the Tahoe Region dropped 13 percent between 2018 and 2022. The decline in VMT resulted in a corresponding decline in VMT per capita, bringing the threshold into attainment. While those results are encouraging, time will tell if they are long term gains or merely a short-term behavioral shift.  

·        Impacts to stream habitat from the Caldor Fire being addressed by restoration work.

Fisheries standards are designed to support the sustainability of fish populations, protect aquatic ecosystems, maintain biodiversity, and protect local economies and recreational activities. There are five adopted Fisheries standards, two are in attainment, one management standard is achieved and adopted into the Regional Plan, and two are in non-attainment. 

Lake Tahoe's fisheries are a vital part of its ecological and cultural heritage, supporting a diverse array of aquatic life and offering recreational opportunities for anglers. Unlike wildlife programs, the Fisheries threshold standards are intended to improve or maintain lake and stream habitat. According to the 2023 evaluation, the region’s streams in “excellent” health are exceeding the target, while streams in “good” and “marginal” health did not meet the threshold target. Threats including wildfire smoke and shifts in the timing and form of precipitation in the region pose a longer-term threat to native fish that may need to be monitored.   

Along with other short-term impacts to threshold standards, the 2021 Caldor Fire negatively impacted streams on Lake Tahoe’s South Shore. Seven sites within the fire perimeter were sampled before and after the fire, and six of those sites were degraded due to fire impacts. Restoration work is occurring on Saxon and Trout Creeks and TRPA and partners will continue to monitor these streams to help prioritize projects for partner agencies.  

While the fisheries standards were found to generally be in attainment, the standards focus on physical habitat requirements to support native fish that may not reflect the status or health of the actual native fish populations. Populations of native fish species are significantly below historic levels, likely the result of the presence of invasive fish. Control of non-native trout species is a priority and is currently occurring in Fallen Leaf Lake and some tributaries such as the Upper Truckee River.  

·        Most monitored species including bald eagles, peregrine falcons, and osprey are showing healthy and active populations.

·        Winter bald eagle surveys recorded the highest population ever observed since monitoring began in 1998.

Wildlife standards help protect habitats, biodiversity, and ecosystem integrity and ensure the long-term survival of valued species. Wildlife standards are intended to enhance the suitability and extent of riparian habitats and maintain and protect special interest species such as bald eagle, osprey, and goshawk. There are fifteen adopted Wildlife standards, five are in attainment and eight are management standards previously achieved by their adoption into the Regional Plan. The status of two Wildlife standards could not be determined due to lack of resources for monitoring. 

Over half of the land area of the Lake Tahoe Basin is designated for protection of listed special status species and TRPA restricts development in these areas. In the 2023 Threshold Evaluation, populations of special interest species are either stable or increasing. There were two new bald eagle nest sites found since the 2019 evaluation and the 2021 wintering bald eagle surveys recorded the highest population ever observed within the Tahoe Basin since monitoring began in 1998. 

Wildlife monitoring in Tahoe for some threshold species is sporadic due to staffing and budget constraints of wildlife agencies. Since 2012, the Tahoe Institute for Natural Science coordinates an annual Mid-Winter Bald Eagle Survey for the Tahoe Basin using community members as citizen science along with professional scientists. Positive trends are showing for those species that are consistently monitored—nesting bald eagles, peregrine falcons, and osprey.

While wildlife species addressed in the existing standards are generally doing well, peer reviewers have raised potential areas for improvement, including the selection of special interest species, ecological and conservation priorities, and revisiting the overall goals for wildlife conservation in the region. Currently, population standards for special interest species are limited to avian species and include five species of raptor.

·        Scenic regulations continue to protect views in the region: 93 percent of scenic resources are meeting targets.

Scenic resource protection helps preserve and enhance the aesthetic, cultural, and environmental value of natural landscapes and scenic vistas in the Lake Tahoe Region. Scenic protection policies prevent the degradation of natural landscapes and ensure that visual impacts from new development are reduced by requiring colors, materials, and architectural elements that are sensitive to both the natural and built surroundings. There are 10 adopted Scenic Resource standards. Nine are in attainment and one policy statement was previously achieved by its adoption into the Regional Plan.  

Overall, 93 percent of the scenic resource corridors and viewpoints are considered in attainment and no resources declined in scenic quality over the past three threshold evaluations. The increasing scores suggest that the EIP, scenic shoreline ordinances, and updated building design standards have improved scenic conditions and community character region wide. More than fifteen miles of overhead utility lines  have been buried underground along scenic roadways in the Tahoe Basin since 2007, including nearly seven miles during this evaluation period. These projects are multi-benefit as they  provide both scenic improvements and reduce wildfire risk. 

Undesignated roadside parking continues to be a scenic concern as more visitors use roadsides for parking to access recreation and vantage points. Roadside parking can block scenic views and degrade the visual quality of designated scenic byways. Improving access to recreation areas through transit and trails and implementing parking management and enforcement strategies are a priority in the basin’s Corridor Management Plans. Recently adopted plans along portions of Nevada State Route 28 and California State Route 89 include parking management programs to control illegal roadside parking. 

·        Some improvement in critical wildlife habitat areas.

·        Stable noise levels in monitored areas.

Noise threshold standards provide community and neighborhood tranquility by reducing or eliminating those activities in the Tahoe Basin that produce prolonged, excessive, or unwanted noise levels. Excessive noise can have serious consequences for public health, wildlife behavior, quality of life for residents, and the experience of visitors. There are 24 adopted Noise standards, eight are in attainment and four are in non-attainment. The status of 12 Noise standards were not determined due to changing monitoring priorities. 

Ambient noise levels in eight out of nine Noise threshold land-use categories are in attainment. Noise monitoring resources were prioritized to collect data to analyze baseline ambient noise standards, which better inform management actions than single-event noise standards. Evaluation of the single-event noise standards against the current zero exceedance criteria has been noted as unrealistic by past peer reviewers—one loud vehicle can exceed the standard and show it as out of attainment. The feasibility of meeting the currently adopted single and cumulative noise event standards should be evaluated to ensure the standards are protective and achievable. For these reasons, most single-event noise standards were not monitored or evaluated.

The Tahoe Science Advisory Council coordinated an independent peer review of the 2023 Threshold Evaluation. Below are links to the documents associated with this Peer Review.

Tahoe Science Advisory Council Peer Review Summary: https://www.tahoesciencecouncil.org/_files/ugd/c115bf_31b21ed8eaa34b50a0e6e481ee00e575.pdf

Appendix A: Peer Review Charge: https://www.tahoesciencecouncil.org/_files/ugd/c115bf_4c627d6f96a645bb974124cd2da4ee50.pdf

Appendix B: Submitted Reviews: https://www.tahoesciencecouncil.org/_files/ugd/c115bf_6cd478314afc44e99bdcb8c1444b5322.pdf

Tahoe Regional Planning Agency - Response to Peer Review Summary: https://www.trpa.gov/wp-content/uploads/Attachment-C-Peer-Review-Summary-and-TRPA-Responses.pdf

Tahoe Regional Planning Agency - Line by Line Responses to Peer Review Comments: PeerReviewAllResponses.pdf