No one knows if we can restore Lake Tahoe’s remarkable water clarity or even if we can halt the decline in that clarity. As we described in last week’s article, there has been a fairly steady reduction in the distance one can see objects below the surface since scientific measurements began in 1968. The depth we could see in1968 was 105 feet, or about 50% greater than today’s depth of about 70 feet. The considerable protection efforts by the Federal Government and the States of California and Nevada since the late 70’s have not yet shown a positive effect in reducing the rate of water quality decline.
But Alan Heyveart, a scientist from University of California Davis, has found evidence in the sediments on the lake bottom that the lake has recovered from pollution before. He has taken core samples of the layers of sediment on the floor of the lake that show water quality was reduced during the Comstock silver mining boom of the late 1800s in Virginia City, when most of the forests of the Lake Tahoe basin were clear cut to provide timber for the mines. When the boom died out and the logging stopped, the forests in the Basin grew up again, and the soil disturbances healed over time. During the first half of the 20th century, the Lake’s water quality and clarity actually improved.
Given this evidence, there is hope that we can stop Tahoe’s decline if we can reduce the unnaturally high levels of nutrients and fine sediments that enter the lake due to human disturbances. Tahoe’s current problems began in the 1960’s when the popular Squaw Valley Olympics triggered a new boom—this time a sharp rise in urbanization in the Tahoe Basin. The construction boom disrupted the watershed’s natural water filtration processes, and the combined effects of soil erosion, nutrient (fertilizer) pollution, and air pollution caused the decline we have measured since the 60’s.
Because watershed restoration efforts to date have not reversed the downward trend of water quality, and because Tahoe is considered a national treasure, State, Federal and Local governments have committed to a new level of cooperative effort to save the lake from turning green. The Lake Tahoe Environmental Improvement Program (EIP) is a model for collaboration between public agencies and the private sector to stop the inflow of pollutants into the Lake. Over 800 restoration projects are being planned, and hundreds of millions of dollars are being raised to fund this massive cooperative effort.
While experts agree that the Lake can recover if we greatly reduce pollution, they urge citizens to be patient. Lake Tahoe holds an extremely large volume of water compared to the size of its watershed. The average amount of time it will take to flush today’s pollutants out of the lake at Tahoe City is 700 years! Because of this extremely long “residence time” for pollutants, the citizens of our communities and the nation must be willing to keep the pressure on to reduce water pollution for decades to come.
The Lake Tahoe Report 004
Air Date: 2003.02.25
Video Segment: What We Are Doing to Save the Lake
Interviewees: Juan Palma (TRPA), Carl Hasty (TRPA), Ed Gee (USDA FS)