Lake Tahoe, the largest alpine lake in North America and known for its clear water, saw a significant improvement in clarity in 2018, reaching an average depth of 70.9 feet thanks to a 10 1/2-foot increase from the year before, the UC Davis Tahoe Environmental Research Center announced Thursday.
Each year, researchers use a 10-inch white disk called a Secchi disk to lower into the water to take 26 readings from January through December. Clarity can change daily, monthly and yearly. One reading in March 2018 exceeded 100 feet of clarity. The average winter clarity, when it is typically best, averaged 73.5 feet.
The five-year average lake clarity is 70.3 feet, nearly a foot more from the previous five-year running average.
“In 2018, Lake Tahoe’s clarity regained the expected seasonal patterns that were disrupted by the extreme conditions of the previous year,” said TERC Director Geoffrey Schladow, a professor of engineering at UC Davis.
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“Clarity was expectedly at its lowest point in summer, and winter and fall had the highest values. Devising strategies to improve summer clarity in the long term is a high scientific priority.”
Spring runoffs in 2018 were far lower and earlier than the wet year of 2017, according to the report.
Public and private partners are working to reduce storm-water pollution from roads and urban areas, and to restore streams and floodplains to minimize fine particles and nutrients from impacting lake clarity.
The effort is seeing results, considering the improved clarity trend over the past 20 years. The ultimate goal is restoring Lake Tahoe to the historic level of 100 feet.
Also, the Tahoe Science Advisory Council is in the process of finalizing a new Science to Action Plan to identify key modeling and monitoring needs “to more fully account for climate change impacts on lake clarity and ecological processes,” the report said.
“Research shows Lake Tahoe and other inland water bodies are warming faster than the oceans and atmosphere,” said Joanne S. Marchetta, executive director of the Tahoe Regional Planning Agency, which funded the analysis. “Seasonal weather extremes will most likely drive greater swings in clarity from year to year in the future, so it’s imperative we continue to invest in the lake’s restoration to combat new and emerging threats.”
Photos courtesy of Wikimedia Commons and UC Davis Tahoe Environmental Research Center.
