The clarity of Lake Tahoe has long been one of the most important indicators of the changing condition of this iconic water body. In 2019, Lake Tahoe’s clarity decreased nearly 8 feet from the previous year’s dramatic 10-foot improvement. The average annual value in 2019 was 62.7 feet. The lowest value was recorded in 2017, when clarity was 60 feet.
Such year-to-year and even day-to-day fluctuations are common. A truer picture of the clarity is often indicated by a five-year running mean, which shows a mean clarity of 67.3 feet, according to the data released by the UC Davis Tahoe Environmental Research Center.
Clarity is measured as the depth to which a 10-inch white disk, called a Secchi disk, remains visible when lowered into the water. In 2019, scientists took 28 individual readings at the long-term index station maintained by UC Davis.