Study: Warming may turn Lake Tahoe green

updated 9:09 p.m. ET March 24, 2008

RENO, Nev. - A new study predicts water circulation in Lake Tahoe is being dramatically altered by global warming, threatening the lake's delicate ecosystem and famed clear waters.

The University of California, Davis study said one likely consequence is warmer lake temperatures that will mean fewer cold-water native fish and more invasive species — like carp, largemouth bass and bluegill.

"What we expect is that deep mixing of Lake Tahoe's water layers will become less frequent, even nonexistent, depleting the bottom waters of oxygen," said Geoffrey Schladow, director of the Tahoe Environmental Research Center at U.S. Davis.

Schladow, Associate Director John Reuter and postdoctoral researcher Goloka Sahoo presented the findings last week in Incline Village at a conference focusing on global warming and deep-water lakes.

The changes, the study concluded, could turn Tahoe's famed cobalt-blue waters to a murky green in about a decade.

"A permanently stratified Lake Tahoe becomes just like any other lake or pond," Schladow said. "It is no longer this unique, effervescent jewel, the finest example of nature's grandeur."

Schladow said researchers are trying to determine if lowered global greenhouse-gas emissions would significantly slow the lake's decline or possibly prevent it.

On average, water in Lake Tahoe — at 1,644 feet deep — mixes every four years, the researchers said.

The water circulation brings nutrients from the bottom to the surface, where they promote algae growth. Oxygen from the surface, meanwhile, is spread through the lake and supports aquatic life.

The new study showed that, if global greenhouse-gas emissions continue at current levels, mixing could become less frequent and less deep, and possibly stop as early as 2019.

"While we expected that the lake would mix less in the future, learning that we may be only a decade or two from the complete shutdown of deep mixing was very surprising." Schladow said.

"If mixing shuts down, then no new oxygen gets to the bottom of the lake, and creatures that need it, such as lake trout, will have a large part of their range excluded," Schladow said.

When the oxygen is gone, the study said phosphorus contained in lake-floor sediments would be released and spur algae growth, further damaging the lake's clarity and water quality.

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