Development Puts Lake Tahoe’s Water Clarity in Peril, 2-Year Study Concludes
Decades of development around Lake Tahoe are exacting a worrisome toll: A white dinner plate used to measure the lake’s clarity was visible at depths of 105 feet in the 1960s but is visible only as deep as 66 feet today.
In another 30 years, the plate would be visible only as deep as 40 feet, a new study suggests, if the decline in Tahoe’s clarity goes unchecked.
“Lake Tahoe is gravely imperiled,” government scientists and university researchers concluded in a report released last month. “The biological integrity of many aquatic ecosystems in the basin appears to be at risk.”
The $2.6-million study was launched two years ago as a result of President Clinton’s environmental summit at the Sierra lake, the largest alpine lake in North America and the second deepest lake in the United States, after Oregon’s Crater Lake.
Several animal species once abundant in the Tahoe Basin are vanishing or lost, including the yellow-legged frog made famous in Mark Twain’s “The Celebrated Jumping Frog of Calaveras County,” the Lahontan cutthroat trout, the Sierra Nevada red fox and the willow flycatcher.
“The scientific evidence suggests that recent human impacts are largely responsible for the current decline in the clarity of the lake,” the report concludes, a decline that clouds the water from its famous cobalt blue hue and could leave it a murky green by 2030.
Dennis Murphy, a biology professor at the University of Nevada, Reno, who helped with the study, said many fear only a decade remains to arrest the loss of clarity “or we may find ourselves with something other than the fabled aqua waters of Lake Tahoe.
“We all seem to agree that at some point with lake clarity, we may cross some threshold and not be able to get back,” he said.
Scientists are still trying to figure out how the many human impacts combine to affect the lake that straddles the Nevada-California border--from the logging of the late 1800s to the housing development boom around the lake in the 1960s and air pollution in neighboring urban centers.
“With perhaps as few as 10 years left to halt or reverse the loss of clarity in the lake, the basin’s entire natural and social system must be considered together,” the report says.
Everything from fertilizer on golf courses and smoke from fireplaces to automobile emissions and home building contributes to the problem.
Tahoe’s clarity declines at a rate of about 1 foot a year as a result of the 5% 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 shore-side erosion and water runoff with phosphorus-rich sediment.
“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,” said John Reuter, associate research ecologist at UC Davis and director of the Lake Tahoe Interagency Monitoring Program.
Current levels of funding for research and monitoring are inadequate, the study says. And efforts in Congress to secure hundreds of millions of dollars to finance additional research and protection measures are critical to reversing the staggering decline.
The researchers concluded that about half the nitrogen and one-fourth of the phosphorous in the lake is deposited there from the atmosphere. They have been unable to confirm the specific sources, but note that nitrogen compounds are largely associated with automobile emissions and phosphorous compounds appear to be tied to wood smoke and road dust.
“Automobile emissions especially is an area that is a real challenge because the populations are booming both to the east and west of us,” said Pam Drum, spokeswoman for the Tahoe Regional Planning Agency in South Lake Tahoe, Calif.
“In the Sierra foothills of California, these folks see Lake Tahoe as in their backyard and they like to be able to drive up for a day or two to recreate,” she said.
The assessment downplays fears that the Tahoe Basin could be the site of a massive wildfire. It says Tahoe’s forests are unnaturally thick and subject to insect attack partly as a result of clear-cutting by loggers more than a century ago and the fire-suppression practices that followed.
Some local activists say the report doesn’t pay enough attention to efforts already underway to combat threats to the lake, from transportation projects aimed at collecting and treating road runoff to building restrictions and the public purchase of sensitive shore-side lands for protection.
“They may have gone overboard in trying to sound the alarm,” said Rochelle Nason, executive director of the League to Save Lake Tahoe.
“A lot of people are concerned and are saying, ‘Gee, does this mean Tahoe is doomed?’ We are telling them no. Tahoe is critically at risk, but it is not doomed,” Nason said.
“There is a lot we know about what needs to be done and we are doing a lot of things to stabilize and restore the lake,” she said.
Steve Teshara, executive director of the Lake Tahoe Gaming Alliance representing casinos and other tourism interests, agrees. But he said the report underscores the importance of securing state and federal funding to carry out the necessary restoration projects.
“Now that the document is out,” he said, “we need to have some of the conversations about how to balance environmental and economic concerns.”
