Lake Tahoe gravely imperiled; staggering loss of clarity continues

Scott Sonner

Tuesday, Feb. 15, 2000 | 12:22 p.m.

RENO, Nev. - Lake Tahoe has lost its ability to cleanse itself and its famous cobalt blue hue will turn a murkier green within 30 years without intense restoration efforts, a long-awaited scientific study concludes.

"Lake Tahoe is gravely imperiled," according to a copy of the report's executive summary obtained by The Associated Press.

"The biological integrity of many aquatic ecosystems in the basin appears to be at risk," the study says.

The $2.6 million study by government scientists and university researchers was launched two years ago as a result of President Clinton's environmental summit at the Sierra lake on the Nevada-California border.

It concludes several animal species that were once abundant in the Tahoe basin are vanishing or have been lost, including the Lahontan cutthroat trout, Sierra Nevada red fox, willow flycatcher and yellow-legged frog made famous by Mark Twain's story "The Jumping Frogs of Calaveras County."

"The scientific evidence suggests that recent human impacts are largely responsible for the current decline in the clarity of the lake," said the report to be made public Wednesday at a news conference at King's Beach, Calif.

"Progress made to date, unfortunately, does not diminish the immediacy and urgency of the problems needing redress," according to the researchers at the University of Nevada, Reno, and the University of California, Davis.

Tahoe's clarity continues to decline at a rate of about one foot a year as a result of the 5 percent annual growth in algae, the 1,200-page study says.

The algae growth has been spurred primarily by atmospheric deposits of nitrogen as well as shoreside erosion and water runoff with phosphorus-rich sediment.

A white dinner plate used to measure Tahoe's clarity was visible at depths of 105 feet in the 1960s. But that same plate is visible only as deep as 66 feet today and would be visible only as deep as 40 feet by the year 2030 if the decline goes unchecked, the report said.

"We now know that once nutrients enter the lake, they remain in the water, and can be recycled for decades. As a consequence, these pollutants accumulate over time and contribute to Lake Tahoe's progressive decline," said John Reuter, associate research ecologist at UC Davis and director of the Lake Tahoe Interagency Monitoring Program.

"The ability of Lake Tahoe to dilute nutrient and sediment inputs to levels where they have no significant effect on lake water quality has been lost," he said.

The report says efforts in Congress to secure hundreds of millions of dollars to finance additional research and protection measures are critical to reversing the staggering decline in lake clarity.

"Current levels of funding for research and monitoring in the areas of best management practices effectiveness, source identification and control and treatment of runoff in the Tahoe basin is inadequate to meet the demands," the report said.

The researchers concluded more than half the nitrogen ending up in the lake during a year comes from atmospheric deposits on the lake's surface, and that direct runoff-runoff from the more urban areas that flows directly to the lake, groundwater and streams contribute between 10 percent and 20 percent each.

"The ability of Lake Tahoe to dilute nutrient and sediment inputs to levels where they have no significant effect on lake water quality has been lost," he said.

The assessment downplays fears that the Tahoe Basin could be the site of a massive wildfire. Clear-cut by Comstock loggers more than a century ago, Tahoe's forests are unnaturally thick and subject to insect attack. After a lengthy drought that ended in the mid-1990s, vast swaths of timber were left dead, leading many to fear a conflagration could sweep the Tahoe Basin.

While chances of fires starting remain high, Tahoe's topography and wind conditions - in addition to firefighting capability in the region - make an epic fire unlikely, the report concludes.

"A lot of people were concerned the whole lake could burn up," Murphy told the Reno Gazette-Journal. "That really isn't the case."

More data gaps exist regarding the best forest management practices needed to restore forest health at Tahoe, Murphy said. But it seems clear that controlled burning will continue to play a key role.

Other findings include:

"It's the consensus among the team that we have a limited amount of time to fix the lake," Murphy told the Gazette-Journal. "If we don't start making measurable headway, we're going to lose our ability to fix the lake in the next decade."