The clarity of Lake Tahoe’s blue waters in 2023 continued its years-long trend of improving during the winter and deteriorating during the summer. The annual clarity report, released today by the University of California, Davis – Tahoe Environmental Research Center, found that winter lake conditions were the clearest observed since 1983 and the 10th best on record, with visibility of 91.8 feet under the surface, compared with 72.2 feet in 2022.
Summer months tell a different story, marking the fifth murkiest on record with an average of 53.5 feet, compared with 68.9 feet in 2022. Overall, the annual average for lake clarity dropped to 68.2 feet from its 2022 value of 71.9 feet.
“It’s important to understand the short-term changes but even more important to be thinking about how this lies in the context of the longer-term trends,” said Alexander Forrest, interim director of the UC Davis Tahoe Environmental Research Center.
UC Davis has been measuring clarity and other health indicators at Lake Tahoe since 1968. Clarity is measured as the depth to which a 10-inch white disk, called a Secchi disk, remains visible when lowered into the water. Lake Tahoe’s clarity is just one measure of the health of the watershed, but measurements of clarity loss in the 1950s and 1960s by UC Davis became central to efforts to protect the watershed from pollution and unplanned development.
UC Davis works with the Tahoe Science Advisory Council and partners across the Tahoe Basin to help inform policymakers and the community on strategies to protect the lake and stabilize the decline in clarity that occurred following mid-20th century development.
In 1969, Nevada and California created the Tahoe Regional Planning Agency (TRPA) to lead collaborative efforts to protect and restore Lake Tahoe, set environmental standards, and better manage growth and development in the region.
“Thanks to the bi-state partnership, Lake Tahoe is one of the most protected watersheds in the nation,” TRPA Executive Director Julie Regan said. “The science community has played a pivotal role in driving environmental restoration, and we’re proud of our collective progress on Lake Tahoe’s clarity over decades. What happens on land affects the lake; we continue to look to science to inform and prioritize restoration projects.”
Under the Lake Tahoe Environmental Improvement Program (EIP), California and Nevada along with more than 80 public and private organizations are actively working to restore lake clarity to its historic level of 97.4 feet. EIP partners have implemented hundreds of projects aimed at restoring wetlands' filtering function and treating stormwater runoff.
The report attributes clearer winter months (December 2022 through March 2023) to deep mixing events that brought clear water from Lake Tahoe's bottom to its surface. Following these clear winter months, runoff and plankton were highlighted as contributing factors for low summer clarity values.