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Lake Tahoe loses 8 feet of clarity in 2019

Lake Tahoe’s clarity took a small hit in 2019 but the overall outlook isn’t all bad. 

In 2019, Lake Tahoe’s clarity decreased nearly 8 feet from the previous year’s 10-foot improvement. The average clarity in 2019 was 62.7 feet, determined by 28 measurements taken over the year at the UC Davis Tahoe Environmental Research Center long-term intake station. 

According to a report from UC Davis, clarity fluctuates year-to-year so the 5-year average shows a better picture and is 67.3 feet. 

The highest clarity value of 112 feet was recorded on February 19, 2019, when the lake mix settled to the bottom for the first time in eight years. 

“When deep mixing occurs, it brings clear, deep water to the surface to immediately improve clarity, but the nutrients that are also moved can produce algal blooms later in the year,” the report said. 

“On its face, this data is startling, but not unexpected,” said Darcie Goodman Collins, the League to Save Lake Tahoe CEO. “After an encouraging 10-foot gain in clarity from 2017 to 2018, the losses from 2018 to 2019 reveal how strongly Tahoe’s blue is tied to the effects of the climate crisis and influenced by the Lake ‘turning over’ or mixing all the way to the bottom. It also spotlights the need for everyone of us – public agencies, environmental organizations, local businesses, visitors and residents – to do all we can to Keep Tahoe Blue.”

The presence of the tiny algal cell Cyclotella was seen in May, which led to the lowest clarity of the year of 36 feet. 

There were also higher than average particle loads washed into the lake from the surrounding watersheds. Warming lake temperatures on the surface keep those particles floating longer, leading to murkier waters in June and July. 

“Understanding why summer clarity continues to decline is our highest priority, and we continue to work closely with the science community to understand how to reverse that decline,” said Joanne Marchetta, executive director of the Tahoe Regional Planning Agency, which funds the clarity report. “We remain committed to the lake’s restoration in the face of the urgent threats of climate change and invasive species.” 

Lake clarity could continue to take a hit in the following years because of the warming climate. More than 80 agencies are working on environmental solutions for Lake Tahoe’s ecosystem. 

“With lake warming impacting the recovery of Lake Tahoe’s clarity, we’re looking for ways that can mitigate climate impacts. Approaches such as the removal of the invasive Mysis shrimp are showing great promise for clarity improvement in the next few years,” said Geoffrey Schladow, director of the UC Davis TERC in a press release. “The environmental services that the natural Tahoe ecosystem provided are now being better recognized.”

“While Mother Nature got a well-deserved break when shelter-in-place orders were in effect, climate change won’t go away that easily,” Goodman Collins said. “The quick recovery we witnessed in air quality and wildlife activity over the last few months should give us hope that by reducing global emissions, the ecosystem will bounce back and Tahoe’s clarity will improve. On a local level, it’s crucial that we are aware of the forces damaging Lake clarity and are actively working to minimize their impacts here in the Basin.”


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