latest news Lake Tahoe could get clearer in the next few years, report says

Lake Tahoe, the world’s clearest large lake, could become even clearer in the next few years due to changes in its plankton population, scientists have said in a new report.

Researchers at UC Davis released their annual report on the state of Lake Tahoe last week, detailing several significant water changes, including a plunging level of Mysis shrimp, a type of zooplankton, which could increase clarity. Lake.

The team of scientists predicted that the declining Mysis shrimp population will have a cascading effect on the lake. The zooplankton species, which is about the size of the width of a fingernail, is known to feast on the lake’s native daphnia, a tiny crustacean that spends much of its time devouring algae that would otherwise would dilute the clarity of the lake, the report says.

Dropping Mysis shrimp numbers could allow daphnia to reassert themselves, increasing the clarity of Tahoe’s water, researchers said. Daphnia are also eaten by kokanee salmon, and if the daphnia population remains high, the size of the salmon could increase significantly, the scientists wrote.

While the improved clarity isn’t a safe bet, the scientists said they’re basing their predictions on a similar situation that occurred in Lake Tahoe’s Emerald Bay about a decade ago, which resulted in a “dramatic” increase in clarity.

“We expect the clarity to improve, but just temporarily,” said Geoffrey Schladow, professor of water resources and environmental engineering at UC Davis.

Schladow said the Mysis shrimp will likely return in a few years, but there are ways for the population to be culled by humans.

The university has continuously monitored Lake Tahoe since 1968. Researchers measure lake clarity by lowering a 10-inch-wide white disk, called a Secchi disk, into the water and marking how deep the disk remains visible.

The average depth at which the disk could be seen in 2021 was 61 feet. Federal and state regulators have set a Secchi depth of 97 feet 4 inches as the lake’s “clarity restoration goal.”

Beyond the appearance of the water, clarity is important because it makes it more difficult for invasive species to reproduce in the lake. It also allows Tahoe residents to drink unfiltered water, which Schladow says could change if the clarity gets worse.

Despite the harbinger of better clarity in the lake, 2021 has also seen massive growth in floating algae near the shore, which the report called a “growing ecological threat to the lake”.

“Blooms also occur where the greatest number of people – residents and visitors – interact with the lake,” the report said. “The abundance of floating algae has also increased by 300% over the past year, reaching a record annual value in 2021.”

Scientists also monitored the lake’s response to a number of devastating wildfires in the area last year, including the Dixie, Tamarack and Caldor fires.

The UC Davis researchers noted that phytoplankton in the lake were rising much closer to the surface than usual, which could be due to lower levels of sunlight due to wildfires. High levels of phytoplankton on the surface of the lake make it harder to filter surface water, the scientists said.

In addition to the wildfires, dry conditions in the region caused the surface of the lake to plummet throughout 2021, with the lake briefly falling below its “natural rim” for an 11-day period.

“It is almost certain that the lake will fall below its natural edge during the summer of 2022 and stop the flow of the river to the Truckee River,” the scientists wrote.

Without flow to the Truckee River from Lake Tahoe, rafting on the river would be limited, Schladow said. It could also negatively affect already endangered fish.