Lake Tahoe Has Clearest Water Since 1980s: Study

Lake Tahoe’s clear-blue water is seen at Zephyr Cove Marina in Nevada April 13, 2023. The M.S. Dixie II tour boat docked at the marina is popular with summer tourists. Jill McLaughlin/The Epoch Times

Lake Tahoe, the largest alpine lake in North America, is the clearest it has been for nearly 40 years, according to a new University of California–Davis study.

In the last five months of 2022, a resurgence of native algae-eating zooplankton cleaned up enough murky debris to restore the lake’s famous cobalt-blue water. The lake could clear up even more in the future, researchers said.

“Clarity may return to 1970s levels—despite the expected large runoff from this year’s record snowpack,” Brant Allen, a local boat captain who helped measure the clear water, said in an April 10 statement.

Lake Tahoe’s clear-blue water is seen at Zephyr Cove Marina in Nevada on April 13, 2023. The alpine lake, which straddles northern California and Nevada, was the clearest it has been in 40 years last year, according to a University of California–Davis study. Jill McLaughlin/The Epoch Times

The lake is world-renowned for its clear, icy blue water and surrounding mountains. It’s the second deepest lake in North America.

According to findings reported in the “Lake Tahoe Clarity Report 2022” released April 10 by UC Davis Tahoe Environmental Research Center, the lake gained nearly 11 more feet of clarity last year. In 2021, the water was clear up to 61 feet. Scientists measured the clarity up to nearly 71.7 feet in 2022.

Restoring the Lake

Agencies in California and Nevada are working together to restore the lake’s clarity to its historic 97.4 feet, according to the study.

Longtime South Lake Tahoe resident Mark Oser grew up on the shores of Lake Tahoe. His mother, who was the first woman Coast Guard pilot on the lake, used to take their old wooden boat to the Cave Rock area on the eastern shore.

“She used to drop a dime down in the water and she could see it go all the way down until it hit the bottom,” Oser told The Epoch Times. “I haven’t been able to see that in a long time.”

In the past few years, Oser said he has noticed the water getting murkier at his neighborhood beach next to Lakeside Marina.

“I was going swimming every day,” he said. “I would get out there and it was gross. You can’t even see your feet. It’s disgusting.”

Algae-Eating Helpers

Researchers suspect the recent growth of zooplankton—small, microscopic animals—is the biggest reason the lake has regained clarity.

Some zooplankton in Lake Tahoe, mostly Daphnia and Bosmina, have consumed enough small single-celled algae particles to start clearing the lake.

“Daphnia and Bosmina largely disappeared from the lake after they were grazed down following the introduction of the Mysis shrimp in the 1960s,” Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center, said in a statement. “In late 2021, the Mysis population unexpectedly crashed, and it took 12 months for the Daphnia and Bosmina to build up their numbers and start their natural cleansing.”

Lake Tahoe’s clear-blue water is seen near Cave Rock on April 13, 2023. The alpine lake, which straddles northern California and Nevada, was the clearest it has been in 40 years last year, according to a University of California–Davis study. Jill McLaughlin/The Epoch Times

A concentration of small particles—such as silt and clay, and algae—has built up around Lake Tahoe’s shores, creating deeper green murky waters.

Large amounts of spring runoff from the lake’s surrounding mountains and warmer surface temperatures also affect the clear water, but the study found that the zooplankton growth was the most important.

“The report examined all these factors and concluded that only the change in the zooplankton community could account for the magnitude of this year’s change,” the study reported.

Researchers expect the clarity to continue improving through this year, the university reported. But if the lake’s population of shrimp rebounds, they could consume the zooplankton and the clarity would be reduced, researchers said.