Risk Factors for Coliform Bacteria in Sierra Nevada Mountain Wilderness Lakes and Streams

In the Sierra Nevada Mountain wilderness backcountry, debate has occurred regarding the impact of cattle, pack animals, and humans on microbial contamination of the watershed. Using coliform bacteria as a marker, we hypothesized that water from high alpine watersheds with more frequent human or animal use patterns would have increased risks for presence of potentially harmful microbes. We analyzed 80 water samples from alpine wilderness areas in the Sierra Nevada Mountains of California for risk of coliform bacteria. The study found coliform bacteria at 92% of cattle sites and 56% of pack animal sites (horses and mules). In contrast, coliform bacteria were found in 18% of human day use areas, and 14% of backpacker sites. Wild sites, without human or domestic animal impact, had an 18% prevalence of coliforms. Differences in prevalence of coliform bacteria between these sites were statically significant. Heterotrophic bacteria counts were also increased in cattle and pack animal use areas. This study suggests that wilderness usage by cattle and pack animals affects water quality. Robert W. Derlet. John R. Richards.