Researchers: Lake Tahoe's worsening clarity leveling

Scientists who for decades reported the famously clear Lake Tahoe to be turning ever murkier have discovered that the decline actually has been leveling since 2001.

Using a new, more sophisticated computer analysis of environmental data on Tahoe, the researchers also found that the shift was not weather-related but more likely the payoff from years of costly and contentious building restrictions to curb polluted runoff into the lake.

"It's a good hypothesis that the land use restrictions and erosion controls have something to do with it," said John Reuter, a lake scientist with the University of California, Davis, Tahoe Environmental Research Center.

The findings, obtained by The Bee, mark the most encouraging development in 40 years of monitoring the clouding of Lake Tahoe, according to Charles Goldman, who in the 1960s was the first scientist to foresee Tahoe's troubles and act on its behalf.

"There's promise in this data that we've crossed the line," said Goldman, a UCD professor,

The Tahoe researchers stop short of calling the post-2000 clarity measurements an "improvement" because visibility continued to diminish, only at a slower rate than that in the previous 33 years.

"The last seven years defies the previous trend," said Geoffrey Schladow, director of the Tahoe research center. It's changing in the right direction."

"That's excellent news," cheered Rochelle Nason, executive director of the League to Save Lake Tahoe, known best for its "Keep Tahoe Blue" bumper stickers.

"We have good reason to believe the measures to protect Lake Tahoe are indeed improving the clarity, and this news supports that."

California, Nevada and the federal government have poured millions of dollars annually into preserving 193-square mile lake - "a noble sheet of blue...not merely transparent, but dazzlingly, brilliantly so," as Mark Twain saw it 136 years ago.

Tahoe still dazzles. But erosion, construction runoff and air pollution have reduced Tahoe's visibility by nearly one third since the development around the lake started to flourish, beginning in the 1960s.

Tahoe has been losing visibility by almost a foot a year on average. The lake's clarity levels fluctuate from year to year, depending on the weather. Visibility dips in colder years with more rain and snow, which leads to more runoff of sediment and fertilizers into the lake. Phosphorus and nitrogen fuel algal growth, which cloud the lake along with road dust and vehicle exhaust particles.

Using a computer model that Schladow developed, researchers filtered out the influence of precipitation on lake clarity to see whether the 2001-2007 leveling of transparency held. To their surprise, it did, confirming that the lake's visibility was on a distinctly new trajectory.

Seven years is too short to predict whether the new pattern will hold, improve or return to the old trend, the scientists said.

But it's long enough to raise hopes of a bluer Tahoe - and more public money towards its preservation, said John Singlaub, executive director of the bi-state Tahoe Regional Planning Agency, which regulates construction in 500-square-mile basin.

"I have to think that the investment we have made to improve water quality and that residents have been making with best management practices on their properties are having a payoff," Singlaub said.