World-renowned for its crystal clear, azure water, Lake Tahoe straddles the Nevada-California border, stretching 22 miles long and 12 miles wide and hemmed in by Sierra Nevada peaks.

At 1,645 feet deep, Tahoe is the second-deepest lake in the United States and the 10th deepest in the world. The iconic lake sits 6,225 feet above sea level.

Approximately 40 percent of the Tahoe Basin’s rain and snow fall directly into the lake, contributing to Lake Tahoe’s legendary clarity. The remaining precipitation drains through granitic soils, which are relatively sterile and create a good filtering system.

Formed by uplifting, glaciation and erosion about 2 million to 3 million years ago, Lake Tahoe today is facing major challenges.

Lake Tahoe Challenges

Lake Tahoe’s vitality is threatened by several factors, including invasive species such as trout and bass, stormwater runoff and increasing temperatures as a part of ongoing climate change. California’s historic five-year drought, which ended in 2017, led the lake to be the driest it had been in a century. But the historic precipitation that followed caused the lake to fill to the brim, making popular beaches smaller in size.

The influx of people and development into Lake Tahoe during the last century adversely affected the lake’s famed clarity. Urban runoff containing such things as fertilizers feeds algae growth in the lake while other sediment flushed into the lake causes it to be less clear. Once in the water, these ultra-fine sediments are one of the primary culprits for loss of clarity as they reflect sunlight.

Experts believe the biggest problem affecting Lake Tahoe’s clarity is algae. Because the lake is a contained body of water with only one outlet, the Truckee River, the lake has difficulty “flushing,” despite inflow from several surrounding creeks.

Meanwhile, many of the basin’s natural wetlands have been filled in to make room for development, which increases runoff into the lake and decreases the natural filtration process provided by wetlands.

Lake Tahoe Restoration Efforts

For more than 20 years, the Tahoe Regional Planning Agency, a joint planning effort between California, Nevada and the federal government, has worked to protect Lake Tahoe by restoring wetlands, preventing contaminants from reaching its shores and monitoring water quality. A summit led by President Clinton in the 1990s helped draw attention to the issues facing the lake.

Returning Lake Tahoe to near-pristine conditions is a long-term effort and requires more work. Researchers use a variety of methods to determine Lake Tahoe’s clarity, including a Secchi disk, a dinner plate-sized object dropped into the lake until it is no longer visible. In 1962, the first year of measurements, the Secchi disk was visible at 136 feet.

Heavy rains in 2016-2017 deposited a massive amount of sand and mud into the lake. Consequently, in 2017, the disk could be seen only at 60.4 feet, the lowest visibility level recorded. In 2019, the University of California, Davis Tahoe Environmental Research Center reported a five-year average in lake clarity of 70.3 feet, an increase of about a foot from the previous five-year average.

Tahoe Regional Planning Agency’s environmental improvement program, financed by nearly $1 billion in local, state and federal funds, aims to restore and maintain the ecosystem health of Lake Tahoe. Projects and programs undertaken by TRPA and other agencies include:

• Replacing 23 acres of wetlands near the mouth of the Upper Truckee River, a $10 million restoration project
• Monitoring the amount of sediment and nutrients flowing into the lake from the Tahoe Basin’s tributary streams and groundwater aquifers
• Constructing rock trenches and retention basins; a $7 million program by the California Department of Transportation to keep stormwater runoff and sediment out of the lake by allowing polluting sediments time to settle out and be absorbed into land

Overall lake health remains a concern and is affected by climate change.

In its 2017 annual report, UC Davis’ Tahoe Environmental Research Center found that the number of days during which Lake Tahoe exhibited summer-like conditions increased by 26 days since 1968. Furthermore, the lake has been warming by one-half degree Fahrenheit each year, which is 14 times faster than the long-term warming rate.

One of Lake Tahoe’s biggest future challenges may not be environmental but managerial. California and Nevada’s joint jurisdiction over the lake has been tested. In 2013, Nevada lawmakers proposed legislation to end the arrangement but ultimately decided to continue the joint jurisdiction.