Lake Tahoe is the clearest it's been since the 1980s, according to new report
Scientists measure a lake's clarity as the depth to which a 10-inch white disk, called a Secchi disk, remains visible when lowered into the water.
With the help of a recently rebounded microscopic animal, Lake Tahoe’s famed blue waters are making their biggest comeback in nearly 40 years.
University of California Davis' Tahoe Environmental Research Center has looked to better understand the physics and ecology of the lake by monitoring its clarity for the past 50 years, which helps to determine and address causes of change.
Researchers attribute the improved clarity to a resurgence of the lake’s native zooplankton, according to the 2022 Lake Tahoe Clarity report released Monday.
“They’ve provided a natural clean-up crew to help restore the lake’s famous blue waters,” scientists said in the report.
Lake Tahoe experienced an increase in algae growth and the presence of very fine particles, such as silt and clay, in the late 1960's through the turn of the century, which led to a decline in clarity, according to the report. The phytoplankton Cyclotella, a single-celled algae, has impacted clarity in most years.
But over the past decade, researchers have seen an improvement in winter clarity.
Using the Secchi disk (a white dinner plate) to measure visibility in the waters, researchers measured the average annual clarity at nearly 72 feet, “the clearest it has been since the 1980s,” according to the report.
Officials in both California and Nevada, which share a border at Lake Tahoe, hope to return the lake clarity to its historic 97.4 feet, the report said.
How do zooplankton change a lake's clarity?
Zooplankton — which began to decline in the 1960s due to the growth of its primary predator, the Mysis shrimp — can help improve the lake’s clarity because they eat clouding particles.
The Daphnia and Bosmina zooplankton species have unexpectedly crashed to dangerously low levels over the years, plummeting to record lows in 2021.
“We expect the impact of Daphnia and Bosmina to grow over 2023, and clarity may return to 1970s levels — despite the expected large runoff from this year’s record snowpack,” said Brant Allen, the research center’s boat captain.
The lake’s particle levels broke a record high in 2021, likely due to wildfires, which lowered its clarity, scientists said. 2021 was also the second-worst clarity year recorded, at a depth of 61 feet. 2017 was the murkiest year.
Scientists that expect a rebound of the Mysis shrimp populations are discussing population control measures to preserve the lake’s clarity.
The Tahoe Environmental Research Center’s 2023 State of the Lake report is expected to be released in July, and they expect the clarity improvement to continue through 2023.
More coverage by Paste BN
- Before and after photos show California reservoirs replenished after historic rains
- 'If I can do this, I can do anything': How this Tahoe nonprofit empowers travelers with disabilities
Camille Fine is a trending visual producer on Paste BN's NOW team.
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