Experts say the 9.5-foot (2.8-meter) decline was most likely due to a convergence of drought, record precipitation and warm temperatures.
The dinner-sized disc used to measure clarity was only visible as deep as 59.7 feet (18 meters). The worst level recorded previously was 64.1 feet (20 meters) in 1997.
Officials at the Tahoe Environmental Research Center say the combination of extreme drought and heavy rainfall washed 12,000 tons of sediment into Tahoe's waters in 2017.
UC Davis engineering professor Geoffrey Schladow says measurements taken so far this year already are showing improvement and are more in line with the long-term trend. The five-year average is approximately 70 feet (21 meters).
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