While the leaders of the Lake Tahoe region deal with the impact of millions of visitors each year and the trash they leave behind, the lake itself is currently the clearest it has been since the 1980s. Researchers from the UC Davis Tahoe Environmental Research Center credit the lake’s native zooplankton, which provide a natural clean-up for the famed blue alpine lake.
In the research center’s latest clarity report, released this year, clarity is measured as the depth a 10-inch white disk, called a Secchi disk, remains visible when lowered into the water. In 2022, Lake Tahoe’s average annual clarity was 71.7 feet compared to 61 feet in 2021. The greatest improvement was between August and December, which coincided with the highest numbers of zooplankton Daphnia and Bosmina.
Zooplankton are small, microscopic animals that consume particles. They disappeared from the lake after Mysis shrimp were introduced in the 1960s. In 2021, the shrimp population declined, which led to a resurgence of the zooplankton.
“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,” TERC boat captain and Secchi disk observer Brant Allen says in a UC Davis news release. “These events support the hypothesis we put forward several years ago that the food web is a major factor in controlling lake clarity.”
Other factors influence the lake’s clarity, such as snow runoff, litter and pollution. Managers of the Tahoe basin report more than 500,000 pounds of sediment and other pollutants are kept out of the lake each year through roadway maintenance. The nonprofit Clean Up the Lake had scuba divers remove more than 25,000 pounds of trash from Lake Tahoe’s 72-mile-long shoreline last year.
California and Nevada, which share a border at Lake Tahoe, are
working to restore lake clarity to its historic 97.4 feet.
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