In the News

Tahoe’s Unique Features Depend on a Fragile Watershed
date posted: December 27 2005

Lake Tahoe Report #112
April 11, 2005
By John Cobourn and Heather Segale

Lake Tahoe is particularly unique for many reasons, partly because its size and volume. It is the largest alpine lake in North America.

Lake Tahoe is 22 miles long and 12 miles wide. “It has a tremendous volume of water,” says Bob Richards, the recently retired skipper of the UC Davis Tahoe research vessel, the John LeConte. “It has enough water to cover California 14 inches deep if you were to tip the lake up and cover the whole state,” he explains. “It ranks as the 11th deepest lake in the world, with a maximum depth of 1,636 feet. That puts the deepest point more than 90 feet below the elevation of Carson City, Nevada.”

The lake was formed more than 2 million years ago by plate tectonics, when the block of crust below the lake sank, forming a huge trough that was dammed up by volcanoes between the north shore and Truckee. “Since the lake formed, as much as 2,000 feet of sediment has accumulated on the bottom in some places,” Richards says.

The world-famous clarity of Lake Tahoe’s water is largely a result of the relatively small size of the lake’s watershed compared to the size of the lake. The lake surface occupies 192 square miles of the watershed’s approximately 500 square miles. Sixty-three streams carry rainfall and melted snow to Lake Tahoe, while only one river, the Truckee River, flows out of the lake.

In large areas that have not been disturbed by human development, water infiltrates into the soil instead of running off the surface. When water can infiltrate through natural forest duff into the soil, erosion is prevented and pollutants are filtered out before ultimately reaching the lake.

“Because of the small watershed and large size of the lake, Tahoe is naturally clear or oligotrophic,” says Richards. Mark Twain described its water in “Roughing It” as, “not merely transparent, but dazzlingly, brilliantly so.”

About 77 percent of the land in the watershed is owned by the American public and managed by the Lake Tahoe Basin Management Unit of the USDA Forest Service. It was proposed in 1900, 1912 and 1918 that the lake become a national park. However, local governments and major property owners successfully quashed these proposals.

Private lands in the basin are extensively developed. There are approximately 43,000 residences, 11,500 tourist accommodations, and 9,600 vacation homes in the Tahoe Basin. On peak weekends in winter and summer, about 300,000 people visit the lake.

Development has occurred mostly since the 1950s, and it has changed the watershed. Erosion caused by the removal of trees; the construction of subdivisions, roads and commercial areas; and the disturbance of sensitive wetlands has contributed the fine sediment and nutrients that have contaminated the lake.

More than 75 percent of the basin’s marshes, 50 percent of its meadows, and 35 percent of its riparian areas have been lost to development. These wet areas, known as stream environment zones (SEZ), provide food and shelter to 260 species of wildlife and fish. They also act as natural filtration systems for the sediment and nutrients contained in runoff from developed areas.

Bob Richards supports the many educational efforts aimed at teaching people how to make their properties function more like the natural ecosystem that existed here before we came. In particular, he encourages property owners to cover bare soil with mulch and healthy vegetation. By doing so, we can keep soil from eroding in rain or windstorms. “If we can do that, we will be doing a lot to prevent the lake from losing its extraordinary clarity in the next 30 years.”

The Lake Tahoe Report is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis Tahoe Environmental Research Center and the California State Water Resource Control Board. For more information, contact Heather Segale, UC Davis Tahoe Environmental Research Center, (530) 583-3279, or logon to www.lteec.org.