LAKE TAHOE, Nev./Calif. – For decades, the UC Davis Tahoe Environmental Research Center has been tracking the clarity of Lake Tahoe with a white disc known as a Secchi disk, lowered into the depths of “Big Blue.” For nearly 60 years, their findings have been released annually in the Lake Tahoe Clarity Report. The most recent report, which contains the data from 2025, was released on Tuesday.
The 2025 report shows that the annual average clarity remains at a plateau, neither significantly improving nor declining compared to previous years. The annual average was 69.2 feet in 2025. That is 7 feet clearer than last year’s average of 62.3 feet, but not statistically different from recent years, mostly due to a continuing trend of relatively low clarity during summer.
Partners are trying to restore the lake clarity to its historic 97.4 feet, which was the average level recorded between 1967 and 1971.
Results in the last ten years:
After decades of steady water clarity loss in the latter half of the 20th century, organized efforts by Keep Tahoe Blue and other partners in Tahoe’s Environmental Improvement Program (EIP) helped stabilize Lake Tahoe’s world-famous water clarity. EIP projects to restore damaged ecosystems — especially in the Upper Truckee River watershed, Tahoe’s largest tributary — have been an effective investment, as have policies to limit urban runoff and improvements to stormwater treatment infrastructure.
However, more understanding and action are needed to restore water clarity to historic levels.
“Clarity matters because the water is our biggest clue about how the Lake is doing,” said Keep Tahoe Blue CEO, Dr. Darcie Goodman Collin. “If we lose the clear water of Tahoe, we lose everything we love about it. Encouragingly, Lake Tahoe’s multi-year averages for water clarity are stable for another year, despite the continuing trend of declining summer clarity readings.”
She said scientific questions that must be answered have to do with the flow and exchange of nutrients near the shoreline, which is where aquatic invasive species make their impact, as well as the effects of algae and tiny organisms called phytoplankton on Lake clarity.
First 10 years of measuring the clarity with the Secchi disk:
“Water clarity rapidly declined through the late 1990s and then leveled off to what we see today,” said Stephanie Hampton, director of TERC and a UC Davis professor in the Department of Environmental Science and Policy. “I know it is tempting to feel hopeful about an average annual 2025 depth that is slightly deeper than last year, but it is not time to celebrate yet. Statistical analysis shows us that this year was not significantly different from last year, and lake clarity has not substantially improved for decades. We are working with our partners across the basin and employing new lines of inquiry and scientific tools to better understand the dynamics at play in this complex, beloved watershed.”
Partly in response to TERC’s early findings on Lake Tahoe’s clarity loss, Nevada and California created the Tahoe Regional Planning Agency (TRPA) through a unique bi-state compact in 1969 to lead the collaborative effort to protect and restore Lake Tahoe.
“Lake Tahoe’s greatest conservation achievements have come from collaborative implementation of science-based solutions,” TRPA Executive Director Julie Regan said. “This clarity report clearly documents progress as well as the challenges we currently face. With more than 80 public and private partners working together, we will continue advancing the restoration of Lake Tahoe’s spectacular environment.”
“We know that fine sediment particles cloud Tahoe’s waters,” added Goodman. “Over the past two-plus decades, investments in programs to limit these particles — from roads, urban areas, and degraded streams and wetlands — have been successful. The UC Davis report reinforces that those ecosystem restoration and stormwater treatment efforts have been good for water clarity. Yet, the data once again shows that stopping fine sediment pollution is not enough to bring back the water clarity lost last century.”
The full report can be found HERE .
