Efforts to keep pollutants out of Lake Tahoe surpass targets

LAKE TAHOE NV/CA – According to the latest data, local government and State transportation agencies have successfully surpassed 2019 pollution prevention targets established to reduce urban stormwater pollution and restore Lake Tahoe’s famous, crystal-clear water. 

Stormwater from roads and urban areas is the primary source of fine sediment particles, which scatter and reduce light, reducing the distance people can see into Tahoe’s depths.  The Lake Tahoe Total Maximum Daily Load (TMDL) Program’s 2020 Performance Report, compiled by the Nevada Division of Environmental Protection (NDEP) and the California Regional Water Board, Lahontan Region (Lahontan Water Board), details the ongoing accomplishments of this bi-state program to restore Lake Tahoe’s famed clarity.

The report found that, in 2019, urban implementing partners collectively reduced fine sediments by 477,000 pounds; this equates to 853 drums (55-gallon) of fine sediment no longer washing into the Lake, surpassing targets for the program. Reductions of nitrogen and phosphorus – which spur algae growth - also surpassed program targets.  The report is available online at: clarity.laketahoeinfo.org/

Launched in 2011, the Lake Tahoe TMDL Program is a science-based plan to restore clarity to Lake Tahoe, by requiring local governments and highway departments at Lake Tahoe to implement pollutant controls to reduce the amount of clarity-harming pollutants that wash into the lake.

Pollution controls include:

  • Use of environmentally friendly wintertime road operations using state-of-the-art technology 
  • Installation of stormwater treatment systems
  • Controlling runoff from homes and businesses

“Local governments and highway departments continue to reduce Lake Tahoe pollution ahead of schedule,” said Lahontan Water Board Executive Officer Patty Kouyoumdjian. “These efforts are ongoing and critical to controlling runoff from roads and urban areas, which cause over 70% of fine sediment pollution impacting the Lake’s clarity.”

“It is very encouraging that our partners are seeing positive results and TMDL implementation is on track,” said Nevada Division of Environmental Protection Administrator Greg Lovato. “Although great progress has been made, we understand that the work is not done, and new data is presenting new challenges. Beautiful, clear water is a trademark of Lake Tahoe and we are highly motivated to continue this restoration work."

While urban stormwater remains the focus of TMDL Program efforts, non-urban sources play an important role in the lake restoration strategy. TMDL agencies continue to work with non-urban implementing partners to ensure results are accurate and comprehensive.  Actions taken to reduce fine sediment particles and nutrients from non-urban sources, (i.e. forestlands, stream channels, and the atmosphere) are tracked and assessed using a set of project performance measures. 

Key results include: 

  • Retrofitting nearly 235 miles of forest road with stormwater runoff controls
  • Decommissioning 9 miles of unpaved roads
  • Sweeping 7,500 miles of paved roads to prevent dust from being deposited into the lake through the air
  • Restoration of 30,000 linear feet of channel to reduce erosion from stream beds and banks. 

Key Trends

In 2019 several factors converged to reduce the five-year running average of lake clarity to 67.3 ft., likely affected by the fact that two of the top four largest precipitation years on record (2017 first, 2019 fourth) occurred in this timeframe. Despite the effect of washing in higher particle loads from the surrounding watershed during these years, the long-term trend of clarity stabilization continues to hold.

The trend in winter clarity values shows slight improvement, likely in response to TMDL program partner efforts that are done in the winter when most of Tahoe’s annual precipitation occurs. However, summer clarity continues to steadily decline. A bi-state committee of scientists led by the Tahoe Science Advisory Council is reviewing the reasons for the difference between winter and summer clarity, with an initial report due to be completed by August 2020.

Identified as a high priority by the two-states and the Tahoe Regional Planning Agency (TRPA), the report aims to provide insights into factors causing differences between summer and winter and investigate how these factors influence lake clarity. Drivers suspected to influence clarity include, biological conditions; lake stratification from water temperatures; stream/lake interactions; and factors such as the timing and delivery of pollutant loads and extreme climate conditions.

A longer term water quality Science-to-Action work plan was developed by the Tahoe Science Advisory Council in response to requests from resource managers in NV and CA. The plan has identified key areas for investigation needed to provide a better understanding of recent clarity values and trends. This ongoing work will specifically investigate the influence of climate change, the associated impacts to lake dynamics, and watershed hydrology that are anticipated as a result.