12 hours ago
Beauty spot famed for its crystal clear water is suddenly becoming murkier... and experts don't know why
The once pristinely clear waters of Lake Tahoe - the freshwater vacation paradise straddling the California-Nevada border - are suddenly become murkier and scientists don't know why.
The annual Lake Tahoe Clarity Report, released Monday by UC Davis' Tahoe Environmental Research Center, found that the lake's clarity in 2024 was 62.3 feet, nearly six feet shallower than it was in 2023.
To determine clarity, researchers have been lowering a 10-inch white disk into Lake Tahoe for nearly 60 years. The depth at which the disc is no longer visible by researchers is considered the clarity level.
Since observations of the lake began in the late 1960s, average clarity has declined by about 40 feet. The clearest reading ever, taken a February day in 1968, was 141 feet deep.
This year's average of 62.3 feet is the third least clear on record and the worst in several years. It has only been surpassed in 2021, when wildfire smoke covered the region, and 2017, when there were many runoff-heavy storms carrying debris into the lake.
'It's not, at this point, noticeably worse. But it's not getting better, and we need to find out why,' said Stephanie Hampton, director of the Tahoe Environmental Research Center, in a statement.
The goal is to get the lake back to a see-through depth of 97.4 feet, which was commonplace throughout the 1980s.
In recent years, there have been massive efforts carried out by the California Tahoe Conservancy, a state agency established in 1984, and environmental organizations to preserve the integrity of the 191-square-mile lake.
Researchers did say there has been progress, with management agencies preventing more than 500,000 pounds of fine sediment and other clarity-harming pollutants from finding their way into the lake every year. This is mainly done through maintaining roads and erosion-control projects.
Even with that success, the lake's waters are still getting murkier, which has convinced scientists there could be something else at play.
'It may be the lake is different than it was 20 years ago, when these policies and practices were implemented,' Hampton said.
'We need to investigate these particles again to find out what kind of particles they are. Are they still mostly sediment? Or are there more algae, wildfire ash or other particles? That may be key to understanding why water clarity is not improving,' she added.
One theory that has gained some traction in the scientific community is that a buildup of microscopic plankton has led to the declining clarity over time.
The report doesn't provide any definitive conclusions with regard to plankton's effect on clarity.
It does point out that 'water clarity tends to be at its highest when phytoplankton are at their minimum densities during the winter season.'
Data from 2024 shows that Lake Tahoe was at most 50 feet clearer in the winter than in the summer, when there were far more plankton in the water.
Scientists have concluded that since clarity levels have stabilized, conservation efforts have worked to a certain extent.
However, they all seem to agree that more work needs to be done to uncover the underlying problem.
'Science-driven policies have underpinned Lake Tahoe's protection for decades, and seeing lake clarity stabilize is an indicator that we are making progress,' said Julie Regan, executive director of the Tahoe Regional Planning Agency.
The agency leads the Lake Tahoe Environmental Improvement Program (EIP), which was formed in 1997.
A coalition made up of EIP, the state governments of California and Nevada, and more than 80 public and private organizations have consistently worked together to prevent sediment from leaking into the lake.
Because this hasn't improved clarity, Regan said the state of Lake Tahoe is 'concerning.'
'We will continue to work closely with the science community to understand where to direct our management efforts next,' she said.
