Sacramento area may be polluting Lake Tahoe

Wednesday, Aug. 18, 1999 | 3:23 a.m.

RENO, Nev. - Top scientists studying Lake Tahoe disagree about whether hard-to-control pollution blown to Lake Tahoe from the California lowlands is contributing to the lake's loss of clarity.

Growing air pollution in the California foothills and in Stockton are playing a significant role in clarity loss, said Dennis Murphy, an environmental researcher at the University of Nevada, Reno.

The pollution combines with water in the lake to make nitrogen and phosphorus, which fuel the algae growth clouding the lake, Murphy says.

If pollution from outside the basin is a significant factor, it may be difficult to restore the alpine lake's clarity, said Murphy, who led a federal team evaluating Tahoe's environment.

"Even if we do the most thorough job possible here in the basin, that's not going to remove the source of some of these pollutants," Murphy said.

Thirty years ago, a white dinner plate in the lake was visible at a depth of 100 feet. Today, it disappears after 70 feet.

Tom Cahill, an expert on Sierra air pollution at the University of California, Davis, disagrees with Murphy.

Cahill, who is on the federal research team with Murphy, argues that the vast majority of pollution fueling the algae growth comes from the cars, road dust and wood smoke surrounding Lake Tahoe itself.

Wally Miller, another University of Nevada scientist involved in the study, says it is possible that both in-basin and out-of-basin pollution share responsibility for the declining clarity.

"My feeling is we don't have all the answers," Miller said. Further study is planned.

Of the estimated 418 metric tons of nitrogen loaded in the lake over a year, more than half comes from the atmosphere. Of the 45.7 metric tons of phosphorus loaded into the lake, 27 percent comes from the atmosphere and 29 percent comes from streams, the new study shows.