LAKE TAHOE — Much of Lake Tahoe's environment has stayed the same or improved during the past 25 years, but the biggie — restoring Lake Tahoe's historic clarity — remains over the horizon, according to a report released last week.
The Tahoe Regional Planning Agency's 2011 Threshold Evaluation Report is a once-every-five-years look at how the agency is doing on environmental goals required by its founding document.
The report provides a basis for the Regional Plan Update's recently released environmental document and is the fifth of the reports issued since the passage of TRPA's 1987 Regional Plan.
This year's evaluation is the first of the reports to receive a scientific peer review, which found that the report is “technically sound and provides a credible basis to support ongoing TRPA policy-making.”
TRPA tracked 151 of its goals, known as thresholds, in the 2011 report. Sixty-three percent of the thresholds have been met, while 37 percent have yet to be achieved. The goals cover everything from noise to wildlife habitat to recreation.
Gains were made in air quality and scenic quality during the past five years, but water quality continues to be a concern.
The lake's clarity during the winter months has shown recent signs of improvement. Summer measurements have not been as promising.
“Summer clarity is showing negative trends and ongoing research findings are needed to understand why winter and summer readings are moving in seemingly opposite directions,” according to the report.
The evaluation recommends continuing existing programs to get erosion-control measures on the ground and encourage redevelopment projects that treat stormwater for fine sediments and nutrients. Researchers have linked the amount of fine sediment, nitrogen and phosphorus entering the lake following development of the basin to the lake's clarity loss.
Lake Tahoe's near shore — an area that has received increased attention because of recent algae blooms — does not have a specific threshold, but soon will, according to John Reuter, associate director of the UC Davis Tahoe Environmental Research Center.
Researchers are using grant funding to develop a standard to measure near-shore water quality, which could be ready by the end of this year.
Reuter said the key phrase for the near-shore quality is “managing expectations” because people's desire to have the near shore completely free of algae is likely not a realistic one.
Farther out into the lake, algae also remains a problem, according to the report. Free-floating algae has steadily increased between 1968 and 2008. The algae declined in 2009 and 2010, but is expected to continually worsen. The algae contributes to Lake Tahoe's clarity loss by absorbing and scattering light. Increased nitrogen and phosphorus are considered the main causes of the increase, according to the report.
In addition to detailing progress on specific thresholds, the report recommends modifying several thresholds to better fit state standards, while revising or eliminating thresholds that are not achievable or enforceable by TRPA.
Any changes to the thresholds would take place after passage of the Regional Plan Update, which is scheduled for December.