Lake Tahoe's clarity showed a third consecutive year of improvement in 2012, but more study is needed to determine if the gains are part of a long-term trend.
The average clarity for Lake Tahoe in 2012 was 75.3 feet, an increase of 6.4 feet from 2011, according to numbers released Wednesday by the Tahoe Regional Planning Agency and the UC Davis Tahoe Environmental Research Center.
The highest reading in 2012 was 107 feet. The lowest reading for the year was 57 feet.
The average figure is made up of 22 Secchi disk readings throughout the year. The readings are taken by lowering a 10-inch white disk into the lake and recording the depth at which the disk is no longer visible.
Winter clarity has continued to show a long-term trend of improvement, while summer clarity has continued to decline, according to a Wednesday statement from the TRPA and TERC.
"We are very excited about the results from 2012, especially within the context of the long-term record for annual and winter clarity," said John Reuter, associate director of the UC Davis Tahoe Environmental Research Center, in the statement. "It is particularly encouraging to see clarity improved during wet years when the amount of fine sediments and nutrients going into the lake is high."
Whether efforts to reduce the amounts of clarity-reducing fine sediment and nutrients reaching the lake via stormwater runoff can be linked to the recent gains requires additional study, according to the statement.
TRPA spokeswoman Kristi Boosman said the numbers speak to the need to continue environmental restoration and erosion-control measures, while adding that a few more years of data are needed to determine whether the improvements are part of a long-term trend.
Laurel Ames, conservation co-chair of the Tahoe Area Sierra Club, cautioned against putting too much stock in one year's readings of a complex issue without additional context, like recent changes to road sand formulas resulting in less fine sediment reaching the lake. Slow spring runoffs during the past couple of years due to colder springs may have also allowed more runoff to infiltrate into the soil before it could sweep fine sediment into the lake, Ames said.
"I think it's hopeful, and that's good, but I wouldn't hang my hat on it," Ames said about this year's clarity numbers.
One concern for the lake's future is obtaining consistent funding for restoration projects to help restore the lake's clarity.
Representatives of local, state and federal agencies each spoke about ongoing funding concerns to the TRPA's Governing Board Wednesday.
The reluctance of Nevada to sell bonds, California's delay in bringing an updated water bond to voters and the end of the Southern Nevada Public Lands Management Act, which has brought millions of federal dollars to the lake for environmental projects, were all noted as concerns for funding future restoration projects.
TRPA spokeswoman Julie Regan said she hoped one potential source of federal funding, a reauthorization of the Lake Tahoe Restoration Act, would be reintroduced to congress within the next few weeks. The first version of the act spurred more than $1.5 billion in funding for environmental projects from private sources, as well as local, state and federal governments.