Top 5 Issues

Five Things Ailing Lake Tahoe

1. Fine Sediment and Runoff

Sand spread on roads in winter is pulverized by cars until the particles become so fine that they are smaller than the width of a human hair. Rain and snowmelt carry these microscopic particles into streams, stormdrains, and along roadways until they eventually enter the Lake. Once in Lake Tahoe, the particles can remain suspended for many years and refract sunlight, thus reducing Lake Tahoe’s once-famed clarity.

Hundreds of quintillions of ultra-fine particles find their way into the Lake in an average year–that’s billions of billions. About 70 percent of these clarity-damaging particles come from driveways, roadways and parking lots. Best Management Practices (BMPs) are required on all developed parcels in order to capture and infiltrate runoff before it gets into the roadway or the Lake. At the same time, state highway departments and local governments are investing hundreds of millions of dollars installing BMPs on roadways. Public agencies and some private property owners are restoring streams and marshes to help naturally filter fine sediment and other pollutants out of the stormwater.

2. Nitrogen and Phosphorus

Algae need a ready source of nutrients such as nitrogen and phosphorus to multiply. For millennia, Lake Tahoe was nutrient-poor because the water was so clean and pure. The result was very little algae floating in the water or attaching to rocks along the shore. Since the 1960s, scientific researchers have been tracking an explosion in the growth rate of algae that is further contributing to Lake Tahoe’s impaired clarity.

More nitrogen is available today mostly because our cars and many older, inefficient wood-burning stoves spew it into the Tahoe Air Basin where it is often trapped over the Lake. More than 50 percent of the nitrogen going into the Lake comes from these local sources and falls into the water through atmospheric deposition where it feeds algae.

More phosphorus is available today mostly because of phosphorus-based fertilizers. The granitic soil of the Sierra Nevada already contains plenty of phosphorus for most plants and grasses, so any additional phosphorus is likely unused by plants and enters the watershed where algae use it to thrive. Phosphorus-free fertilizers are readily available and TRPA is phasing out the sale of phosphorus-based fertilizers in the Tahoe Basin.

3. The Great Building Boom and Its Legacy

The TRPA capped development in the 1980s, but a massive development boom through the 1950s and 1960s did damage to Lake Tahoe’s ecosystem that could take generations to repair. About 75 percent of Lake Tahoe’s marshes–essential to clean water and habitat–were filled in and 50 percent of meadows were built on. Additionally, buildings and roads were constructed without environmental design or sensitivity to wildlife and the soft, granitic soil of the Tahoe Basin. With an urban boundary firmly in place today and cutting-edge design requirements on all future projects, the challenge today is encouraging environmental redevelopment of these aging buildings and outdated infrastructure.

4. Cars and How People Get Around

Most development in the Tahoe Basin was planned and designed around the private automobile. Neighborhoods were built far from essential services like grocery stores and schools. Commercial centers were designed for convenient parking and less walking; and bicycling was not even an afterthought. As noted above, vehicle emissions have a significant effect on Lake Tahoe’s purity. They also harm air quality and visibility. Updating the design of our town centers and transportation corridors is essential to restoring Lake Tahoe and helping make our communities more walkable, bikeable and sustainable.

5. Imminent Threats

The threats of catastrophic wildfire, introduction of aquatic invasive species, and climate change are among the imminent dangers to Lake Tahoe’s fragile ecosystem that need to be addressed if we are to continue protecting and preserving this national treasure.