(KTXL) — The famous blue water of Lake Tahoe is the clearest it has been since the 1980s, and it’s all thanks to a tiny animal whose population has made a resurgence, according to a new report.

The 2022 Lake Tahoe Clarity Report was released Monday, and it shows that the clarity of the water greatly improved from 2021, but the findings during the last five months of 2022 show that the water reached the clearest level in four decades.

The clarity of the water is measured by the UC Davis Tahoe Environmental Research Center.

Scientists attach a white, 10-inch disk called a ‘Secchi disk’ to the end of a rope and see how low that disk can go into the water before it can no longer be seen from the surface.

In 2022, the average annual clarity was 71.7 feet, meaning that the disk was still visible when it was that deep in the water. In 2021, the average annual clarity was 61 feet.

(UC Davis TERC)

However, it was between August and December 2022 that the average depth where the Secchi disk could still be seen was 80.6 feet, a figure that had not been reached since the late 1980s.

Lake Tahoe water is clearer because of zooplankton

Scientists are attributing the improving clarity to the resurgence of zooplankton, a microscopic animal that is native to Lake Tahoe.

The zooplankton —specifically, the Daphnia and Bosmina— feed on smaller phytoplankton, Cyclotella, a type of algae that makes water murkier.

But in recent decades, the number of Daphnia and Bosmina went down ever since the 1960s, when Mysis shrimp was introduced, which eats the two zooplankton.

Basically, the water of Lake Tahoe has been getting murkier because the shrimp have been eating the animals in charge of cleanup.

Geoffrey Schladow, director of the Tahoe Environmental Research Center, said in a statement, “In late 2021, the Mysis population unexpectedly crashed, and it took 12 months for the Daphnia and Bosmina to build up their numbers and start their natural cleansing.”

Scientists say there are other things that can affect the water clarity, but their report concluded that the only recent change that could have improved the water so greatly is the change in the number of zooplankton.

At the same time, the help that the lake is getting from Daphnia and Bosmina could be short-term due to the possible resurgence of the Mysis shrimp.

California and Nevada, whose mutual border cuts through the middle of the lake, work together on the lake’s health and are trying to restore the lake clarity to 97.4 feet.

Scientists say that, while there are major efforts to keep sediment and pollutants out of the water, the wildlife in Lake Tahoe is just as important to maintain healthy water clarity.

Brant Allen, a boat captain that is part of the research center team, said, “These events support the hypothesis we put forward several years ago that the food web is a major factor in controlling lake clarity.”