A new report by Nevada’s Division of Environmental Protection and California’s Regional Water Quality Control Board, Lahontan, finds that local governments and state highway departments at Tahoe are exceeding targets to reduce stormwater pollution and restore the lake’s famous clarity.

According to the Lake Tahoe Total Maximum Daily Load Program 2017 Performance Report, Caltrans, Nevada Department of Transportation, City of South Lake Tahoe, and El Dorado, Placer, Douglas, and Washoe counties collectively reduced fine sediment stormwater pollution by 12 percent from 2004 baseline levels—exceeding a 10 percent target set for the first five years of the Lake Tahoe Total Maximum Daily Load (TMDL) Program.

Launched in 2011, the TMDL Program is a science-based plan to reduce fine sediment, nitrogen, and phosphorus pollution that harms Tahoe’s clarity and restore lake clarity to 97.4 feet by 2076.

“Local governments and highway departments are doing tremendous work to reduce stormwater pollution that harms lake clarity,” said Lahontan Water Board Executive Officer Patty Kouyoumdjian. “Because of this work, more than 268,500 pounds of fine sediment particles—which equates to about 70 dump truck loads—will no longer wash into the lake each year. The accomplishment of this first round of reductions is a major milestone for Tahoe.”

Fine sediment particles from roads and urban areas are the largest cause of declines in Tahoe’s water clarity. When the tiny particles wash into the lake with stormwater, they remain suspended in the lake and scatter light, reducing its clarity.

To reduce fine sediment pollution, local governments and highway departments have reduced the amount of sand and traction abrasives applied to roads, increased street sweeping, built infrastructure to capture and treat stormwater from urban areas, and upgraded Tahoe’s roads to reduce the amount of polluted stormwater runoff reaching the lake.

Local governments and highway departments also reduced the amount of phosphorus and nitrogen pollution reaching Lake Tahoe by 8.5 percent and 6 percent over the last five years. Phosphorus and nitrogen are nutrients that can trigger algae growth in the lake.

Forested uplands in the Tahoe Basin are estimated to contribute more than a quarter of the total phosphorus loading into Lake Tahoe, while atmospheric deposition from vehicle emissions is responsible for most nitrogen loading into the lake.

Local, state, and federal land and resource management agencies have restored thousands of feet of stream channel and restored hundreds of acres of marshes and wetlands to reduce the amount of fine sediment and nutrient  pollution reaching Lake Tahoe. The performance report finds they are meeting TMDL pollution reduction goals for non-urban areas.

“Reducing pollutant loads from non-urban sources remains an important part of restoring Lake Tahoe’s historic clarity. Our review of the accomplishments over the past several years indicates that implementation efforts remain on track with TMDL established goals,” said Bradley Crowell, director of the Nevada Department of Conservation and Natural Resources.

Lake Tahoe’s water clarity declined by one foot a year on average for several decades, reaching an all-time low of 64 feet in 1997.

Water-quality projects implemented through TRPA’s Environmental Improvement Program helped partners meet pollution reduction goals for the first five years of the TMDL and meet the program’s first clarity restoration target of 71 feet of clarity by 2016.

The five-year average for Tahoe’s clarity was 73 feet in 2016, a 5-foot improvement since the TMDL Program started. Local governments, state highway departments, and land and resource management agencies will have to continue to reduce stormwater pollution and restore important natural areas like streams, marshes, and wetlands to continue making progress on the Tahoe Clarity Challenge.

The TMDL requires additional reductions in the amount of fine sediment, phosphorus, and nitrogen reaching Lake Tahoe over the next five years. And the next interim clarity restoration target is a five-year clarity average of 78 feet by 2026.

“Restoring Lake Tahoe’s famous water clarity requires concerted action around the Tahoe Basin. Meeting this first round of TMDL pollution reduction targets and the first clarity restoration target shows that the Tahoe Partnership is strong and working,” said Joanne S. Marchetta, TRPA executive director. “Achieving lake clarity and many other watershed goals will only be possible through continued partnership and collaboration.”

Tom Lotshaw, Tahoe Regional Planning Agency
From the Winter 2017 edition of Tahoe In Depth