2 days ago
- Science
- San Francisco Chronicle
Lake Tahoe is getting murkier — and scientists don't know why
Lake Tahoe 's famously clear blue waters became noticeably murkier in 2024, ranking as the third least clear on record — and the worst in several years — according to a new report from UC Davis researchers who have monitored the lake for decades.
The annual Lake Tahoe Clarity Report, released Monday by the university's Tahoe Environmental Research Center, found the lake's average clarity last year was 62.3 feet — nearly six feet shallower than in 2023.
That level of clarity was surpassed in cloudiness only by 2021, when wildfire smoke blanketed the region, and 2017, a year marked by runoff-heavy storms.
'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 center and a professor at UC Davis, in a statement.
Clarity is measured using a white Secchi disk, which researchers lower into the water to determine the depth at which it disappears. Since the late 1960s, when scientists began monitoring the lake, average clarity has declined by about 40 feet.
In recent decades, government agencies and conservation groups have invested heavily in efforts to protect the lake's transparency — from restoring wetlands to improving stormwater systems. The report notes some success: more than 500,000 pounds of sediment are now prevented from reaching the lake each year.
Still, summer clarity continues to deteriorate, and researchers suspect new, less understood factors may be driving the trend.
'It may be the lake is different than it was 20 years ago, when these policies and practices were implemented,' Hampson 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.'
One emerging theory is that microscopic plankton, too small to have been tracked in earlier studies, could be contributing to the persistent murkiness.
As climate change ushers in longer, warmer summers, scientists warn that shifting conditions may be reshaping the lake's ecology. At the same time, they say that new development around the Tahoe Basin continues to stir debate about the region's ability to absorb growth without further degrading its signature waters.
'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, in a statement. 'However, the lack of improvement is concerning, and we will continue to work closely with the science community to understand where to direct our management efforts next.'
