Lake Tahoe's clarity improved for the second straight year in 2012, according to a report released Wednesday by UC Davis researchers. But long-term trends indicate climate change is working against that clarity.
The lake's annual "health exam" included predictions for Tahoe in the 21st century, which researchers say could be used to estimate conditions for other lakes in the western United States.
Annual average clarity rose to 75.3 feet 6.4 feet better than the year prior and approaching the clarity target of 78 feet. Researchers attribute the change to less rain bringing fewer watershed pollutants, a lack of surface waters mixing with deep waters and fewer microscopic algae.
But more startling is that Tahoe's snowpack is disappearing, said UC Davis Tahoe Environmental Research Center director Geoff Schladow. The 2013 State of the Lake report included a predictive chart showing dramatic snowfall decreases with warmer weather.
"Right now, the snowpack provides free storage of water," Schladow said. "With more rain and less snow, we'll overflow reservoirs."
The report predicts temperature increases as high as 10 degrees, more droughts and more floods.
The last major Tahoe flood was in 1997, and Schladow said "the likelihood of that happening again is much greater."
Specific to the lake, researchers also say the surface level is more likely to drop below the rim for extended periods. And with the surface water warming up, it'll have increased difficulty mixing with the bottom of the lake.
This could result in a complete depletion of oxygen at deeper levels below 200 meters starting the year of 2065 with increased sediment and loss of habitats.
"That's a scary prospect," Schladow said. "We've never seen the disappearance of oxygen until now."
Because of these findings, monitoring oxygen is even more crucial.
A new system off the west shore provided data 600 meters deep every 30 seconds for this report.
One of Schladow's greatest concerns is the periphyton attached algae turning rocks green around the shoreline.
"Twenty years ago, the rocks were pretty clean," he said. "That's changed. They're slimy."
Schladow said he hopes funding can be secured to implement a new monitoring system next year. The change is disconcerting in part because the shore is what most people immediately experience. No one wants tourists slipping on rocks and suffering injuries. But it also generally indicates that something unusual is happening, and Schladow is puzzled.
"For a long time, it was all about keeping Lake Tahoe blue," he said. "That's still important, but people are now talking about the shore, too."
UC Davis researchers have been monitoring Lake Tahoe since 1968 to measure progress toward Tahoe's restoration. Funding came from UC Davis, grants and private donors.
So what can citizens do? Schladow admitted that at the local level, not much can be done to fight climate change. But for Lake Tahoe, the oxygen levels are increasingly important, and visitors and residents can help by not polluting the water.
Call The Bee's Janelle Bitker, (916) 321-1027. Follow her in Twitter @JanelleBitker.