Scientists Have Spent Billions to Improve Lake Tahoe’s Clarity. It’s Only Getting Worse.

Lake Tahoe’s clarity is its most notable attribute. In the early 1900s, scientists gushed about being able to see 100 feet down into Big Blue, making it one of the most stunning lakes on the planet. In the century since, that clarity has gotten much worse, and despite scientists putting billions of dollars into its recovery, nothing is working.

Not only is Tahoe’s clarity a visual marvel, it also indicates the health of the lake. The marshes on each side of the lake act as a sort of filter for the water, creating a unique clarity. Many factors can contribute to its clarity, or lack thereof, but everyone seems to agree that it’s the central milestone to determining the health of the lake’s ecosystem.

When scientists at UC Davis began testing Tahoe’s clarity in 1968, it sat around 95 feet. The clarity can change depending on the annual precipitation at the lake, but it typically only varies about 20 feet of its average clarity marker. For example, in 1981, the clarity sat at a whopping 100 feet. Just two years later in 1983, the water sat at 58 feet clarity. The natural clarity movement is normal, but it’s trending in the wrong direction.

Scientists at UC Davis released their 2021 Tahoe clarity outlook, which showed the lake at 60 feet clarity last year. Their 54-year study of the lake show the clarity is worsening, despite spending $2.6 billion on projects to protect and preserve Tahoe. The trend is perplexing scientists.

“The lake itself is changing internally, and the external inputs that impact clarity and lake health are changing at the same time,” said Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center. “We are working with other researchers at Lake Tahoe and with agency partners to not only keep track of clarity, but to adapt management approaches for improving clarity in future years.”

Lake Tahoe’s average annual clarity in 2021 was 61 feet compared to 63 feet in 2020. Summer measurements were 54.8 feet, while winter averages were 71.9 feet. While clarity in winter months is invariably better than during the summer, the trend from the past two decades indicates that neither summer nor winter clarity levels are improving over time.

UC Davis scientists plot the average fine particle concentration in Lake Tahoe monthly. Note the spike in 2017, with average concentrations elevated to the present day. (UC Davis Tahoe Environmental Research Center)

Decades of research have shown that small particles and algae are to blame for the clarity of the lake. In fact, even though the weather and other variables have an impact, particles make up 70 percent of the clarity results. Scientists have spent the past 25 years attempting to reduce small particles entering the lake, but have so far failed. Small particles and clarity reached their worst in 2017.

“Extreme weather events and changing lake dynamics are making our investments in water quality even more important,” Tahoe Regional Planning Agency Interim Executive Director John Hester said. “With strong partnerships in the Tahoe science community, we will continue to increase our understanding of how climate-driven changes could be impacting the plan to restore lake clarity.”

So what can be done to restore Lake Tahoe’s clarity to 97.4 feet? No one really knows. Despite 80 agencies in California and Nevada spending nearly $3 billion to improve the clarity of our beloved lake, it’s only gotten worse.

Active NorCal

Telling the Stories of Northern California


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