SOUTH LAKE TAHOE, Calif. — 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, officials say recent data shows.

Stormwater from roads and urban areas is the primary source of fine sediment particles, which scatter and reduce light, reduces water clarity.

The Lake Tahoe Total Maximum Daily Load Program’s 2020 Performance 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.

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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 to implement pollutant controls to reduce the amount of clarity-harming pollutants that wash into the lake.

Pollution controls include:

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· 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 in a press release. “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 in the release. “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

The reducation in the five-year average of lake clarity to 67.3 ft. was likely affected by large precipitiation years in 2017 and 2019.

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.

The report aims to provide insights into factors causing differences between summer and winter and investigate how these factors influence lake clarity, which is a high priority for both states, as well as the Tahoe Regional Planning Agency. 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 Nevada and California. The plan has identified key areas for investigation needed to provide a better understanding of recent clarity values and trends.

This ongoing work will investigate the influence of climate change, the associated impacts to lake dynamics, and watershed hydrology that are anticipated as a result.