Crystal-clear Lake Tahoe is threatened by runoff

Crystal-clear Lake Tahoe is threatened by runoff

By Ben ArnoldyThe Christian Science Monitor

SOUTH LAKE TAHOE, Calif. — With the Angora wildfire contained, officials are now racing to stave off damage to the famous, cobalt-blue Lake Tahoe.

In just over a week, the fire burned 3,100 acres, forced the evacuation of 3,500, and cost $11.3 million to fight. Property losses from more than 325 homes and structures could tack an additional $150 million onto the tab.
Long after the embers fade, the fire is expected to affect the clarity and health of North America's largest alpine lake. Its stewards are scrambling to prevent runoff from the burn area, an effort that could be complicated by community frustration with past anti-erosion regulations.

"Lake Tahoe is revered for its cobalt blue, clear water," says Charles Goldman, a lake researcher at the University of California, Davis. "It's one of the clearest large lakes in the world, even with the transparency loss in recent years."

The lake has lost a third of its transparency since Goldman began monitoring it in 1959. Visitors can still see 22 meters (about 72 feet) down, but that figure shrinks by about one foot each year. Auto exhaust, smoke, road dust and runoff from nearby development are to blame.

That runoff may be accelerated by the fire's destruction of the vegetation that holds soil in place, bringing fine particles into the lake.

These effects aren't merely aesthetic. In the long run, the deep-water oxygen needed for the lake's trout could diminish, Goldman says.

"It's kind of like the canary in the coal mine: We've used water clarity as a symbol of whether the whole lake ecosystem is getting better," says Michael Donahoe, conservation co-chairman with the Tahoe Area Sierra Club.
A greater threat, however, is erosion. The burn area covers 10 percent of the Upper Truckee River watershed, and 25 percent of all water and pollutants entering the lake come from that river, says John Reuter with the Tahoe Environmental Research Center at UC Davis.

The Forest Service, state officials and local planners are working on erosion-mitigation strategies. Even during the firefighting effort, trenches known as water bars were dug to manage runoff. Next steps include planting trees, such as willows, to hold together steep, burned-out slopes.

"The critical time is between now and when we get the rains in the fall. We need to get the planting done," Donahoe says.

While most of the burned land is public, experts say homeowners also have a role to play by replanting properties with vegetation that isn't highly flammable and that retains moisture.

Tahoe residents are familiar with such calls: For decades the Tahoe Regional Planning Agency (TRPA) has strictly managed building and landscaping on properties around the lake with an eye to conserving lake water quality.

The fire stirred up local bitterness, with some residents who think the planning agency exacerbated the fire with an anti-erosion measure that involved keeping a layer of pine needles or wood chips on properties.
Many factors contributed to the fire, including drought, high winds, sluggish efforts to remove brush and human carelessness. Investigators are searching for those responsible for the illegal campfire that started the blaze.
"I think the level of pine needles had very little impact on the course of how this fire burned," Reuter says. "... The best we can do is try to educate people" despite the mistrust.

Elsewhere on Wednesday, an evacuation order was lifted for a string of small northeastern Utah communities as more than 700 firefighters worked to tame a wildfire that has burned nearly 66 square miles.

The fire is burning on public and private land, including parts of the Ashley National Forest, 100 miles east of Salt Lake City. It was about 50 percent contained.

Copyright © 2007 The Seattle Times Company