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Extreme Weather Dropped Lake Tahoe Clarity To Historic Lows In 2017

UC Davis / Courtesy

Tahoe Environmental Research Center boat captain Brant Allen lowers a Secchi disk from the research vessel into Lake Tahoe. The disk has been used for more than 50 years to measure water clarity at the lake.

UC Davis / Courtesy

Lake Tahoe was a lot murkier last year.

Numbers out Wednesday show clarity in 2017 was the lowest on record, but researchers know why it was so bad. 

"It was really the coincidence of some extreme events," says Geoffrey Schladow, who heads the UC Davis Tahoe Environmental Research Center.

Those extreme events were an historic, five-year drought followed by one of the wettest winters on record with mega snow and rain.

All that precipitation flushed sediment that had been accumulating in stream beds during the drought into the lake.

"As an example, in 2017 there was something like 12,000 tons of sediment washed into Lake Tahoe," says Schladow. "In the previous five years, each year had less than a thousand tons. So it's a huge difference."

The average clarity level in 2017 was only 59.7 feet.

"That's about 9.5 feet less than the previous year," says Schladow. "Prior to this the lowest was in 1997, that was 64.1 feet. This notion of multiple extreme events back to back was considered unlikely, but it happened."

Measurements for 2018 have already shown a big improvement more in line with long-term trends.

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