Lake Tahoe report: Removing invasive shrimp boosts clarity

Lilyana Allen uses a telescope Thursday to view Lake Tahoe from an observation platform in Lake Tahoe, Calif. A report says removing an invasive shrimp from the lake could offset a decline in clarity.

RENO, Nev. (AP) — A new report on the progress of efforts to protect Lake Tahoe says removing an invasive shrimp from the alpine waters could offset a decline in clarity while experts grapple with other threats exacerbated by global warming.

Introduced to the lake in the 1960s, Mysis shrimp are driving out native zooplankton that keep the water clear by consuming algae and other tiny particles.

Researchers noticed that removing the shrimp from the lake’s west shore near Emerald Bay resulted in dramatic improvements in clarity. Now they want to expand removal efforts across the lake.

“Lots of things are going to happen here on account of climate change,” said Geoffrey Schladow, director of the Tahoe Environmental Research Center. “With all those things happening, I strongly believe having the native zooplankton will keep the lake clear.”

The findings were a bright spot in the center’s annual State of the Lake report, which documents progress and setbacks in efforts to preserve the largest alpine lake in North America. The Tahoe Basin on the California-Nevada border attracts tens of millions of visitors each year.

The report forecasts greater challenges largely because global warming is driving up temperatures in the basin.

“We’re getting used to that it is on average getting warmer most years, and that is going to keep happening,” Schladow said. “We are trying to do our best to live with it.”

The surface water temperature in Lake Tahoe has been on the rise since at least 1968, when regular measurements began. In 2018, the average surface temperature was 53.2 degrees, the second-highest reading to date, and the lake marked the highest observed maximum daily surface temperature of 77.5 degrees. Warmer water slows down circulation within the lake, meaning it takes more energy to mix warm surface water with cooler water below. Less mixing means a greater buildup of nitrates.

Overall clarity in Tahoe increased 10.5 feet to 70.9 feet in 2018, an improvement, but still short of the goal of 97.4 feet. The 2018 improvement was attributed in large part to efforts by lakeside communities to reduce sediment runoff.

Copyright 2019 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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