Data collected by experts from the UC Davis School of Medicine have revealed that except for some heavily used areas, streams and lakes in the high country of the Sierra Nevada are generally clean and fresh.
The good news for campers can be found in a pair of studies published in the latest issue of the quarterly medical journal Wilderness and Environmental Medicine. UC Davis physician Robert Derlet and pathology researcher James Carlson present data gathered from nearly 100 locations throughout the Sierra Nevada during the summer of 2003, including Yosemite, Sequoia and Kings Canyon national parks. Their goal was to analyze wilderness water quality for the presence of harmful bacteria such as E. coli, which is typically an indicator of contamination from human or animal waste.
Running counter to popular belief, the two researchers downplay the risk of picking up Giardia in backcountry drinking water. In the Sierra Nevada, E. coli and other pathogenic bacteria may pose a greater risk than Giardia for causing waterborne illnesses in people.
"What's impressive is that more than half of our water sampling sites had no water quality problems whatsoever," said Derlet, a professor of emergency medicine at the UC Davis School of Medicine and an avid backpacker with 30 years of experience hiking in California's high Sierra. "People still should use water filters or purification techniques like boiling drinking water in the backcountry. But our findings also are an indication of the outstanding job done by National Park Service in its wilderness management."
Derlet has spent the past five years on water quality studies in the Sierra Nevada. From his recent sampling sites, only 17 had levels high enough to be directly linked to recreational use or the presence of livestock.
"For these two studies, we looked at nearly 100 streams and lakes over the 400-mile long mountain range," observed Derlet, who has given presentations to wilderness rangers about infectious diseases and backcountry medicine. "We've also analyzed water at many more Sierra Nevada lakes and streams this past summer with consistent results. It's not surprising that waterways below roads, popular trails and well-used cattle grazing areas often show the presence of harmful bacteria. However, it will probably take a number of years and some sustained funding to pinpoint the exact causes."
The UC Davis physician says his studies are only a snapshot in time, and that all streams and lakes tested in wilderness areas typically contain a certain amount of naturally occurring aquatic bacteria. Low levels of coliform bacteria actually can be part of the natural environment. If bacteria were not present in the water, it would jeopardize the balance of the aquatic ecosystem, including everything from frogs to fish.
Currently working with renowned Lake Tahoe expert and UC Davis professor Charles Goldman, Derlet has several other water quality findings in the Sierra that he also hopes to research:
- Lakes are typically 'cleaner' than creeks, possibly because the ultraviolet rays of sunlight work better at killing off bacteria in calm waters of a lake than in the tumbling flows of a stream;
- Algae growth in backcountry waterways appears to be getting worse;
- Bacteria readings appear higher at the beginning of spring runoff rather than later in the summer when water levels are lower and water quality is thought to be poorer;
- Valley air pollution could be contributing to water quality problems in the Sierra Nevada.
To view or download the two studies, "An Analysis of Wilderness Water in Kings Canyon, Sequoia, and Yosemite National Parks for Coliform and Pathologic Bacteria" and "Coliform and Pathologic Bacteria in Sierra Nevada National Forest Wilderness Areas Lakes and Streams" on the Web at: https://www.ucdmc.ucdavis.edu/newsroom/releases.
Readers also can get information about other issues in wilderness medicine by visiting the Wilderness Medical Society at https://wms.org/
The studies were supported in part by a grant from the Wilderness Medical Society, with assistance from the U.S. National Park Service.