SACRAMENTO, Calif. _ As director of the emergency room at the University of California Davis Medical Center, Robert Derlet always wondered what made people sick.
Each summer, on hiking trips into the high Sierra, he brought that curiosity along, asking himself: Where do you get infections in the wilderness? The most obvious possibility, he thought, was the water.
Now, after 10 years of fieldwork and 4,500 miles of backpacking, Derlet knows for sure. What he's learned _ after analyzing hundreds of samples dipped from backcountry lakes and streams _ is that parts of the high Sierra aren't nearly as pristine as they look.
Nowhere is the water dirtier, he discovered, than on U.S. Forest Service land, including wilderness areas, where beef cattle and commercial pack stock _ horses and mules _ graze during the summer months. There, bacterial contamination was easily high enough to sicken hikers with Giardia, E. coli and other diseases. In places, slimy, pea-green algae also blossomed in the bacteria-laden water.
Overall, the worst water quality he found was on the Stanislaus and Humboldt-Toiyabe national forests, north of Yosemite National Park. Elsewhere, particularly at high elevations in Yosemite and Sequoia and Kings Canyon national parks, Derlet found a striking difference: Most lakes and streams were as clear as champagne and pollution-free.
The contrast has prompted Derlet and Charles Goldman, the director of the UC Davis Tahoe Research Center, to mount a publicity campaign calling for dramatic management change in the Sierra. Cattle, they say, should be moved to lower elevations, and Forest Service areas where they now graze should be turned into national parks.
"At one time, cattle were important for developing civilization here," said Derlet. "But now, with 40 million people in California, the Sierra is not for cattle. It's for water. We need water more than Big Macs."
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