Park management of the Whiskeytown National Recreation Area, in northwestern California, identified a critical need to determine if mercury (Hg) or other elements originating from abandoned mines within the Upper Clear Creek watershed were present at concentrations that might adversely affect aquatic biota living within the park. During 2002–03, the U.S. Geological Survey, in cooperation with the National Park Service, collected aquatic invertebrates, amphibians, and fish, and analyzed them for Hg, cadmium, zinc, copper, and other metals and trace elements. The data from the biota, in conjunction with data from concurrent community bioassessments, habitat analyses, water quality, and concentrations of metals and trace elements in water and sediment, were used to identify contamination “hot spots.”

In 2002, we selected collection sites within the study area based on the presence of historical mines and results from sampling of bed sediment in 2001. In 2003, collection sites were selected based on sediment data as well as data on water and biota from this study in 2002. Eleven sites were sampled in both 2002 and 2003, 11 sites were sampled only in 2002, and 14 sites were sampled only in 2003.

Comparisons of sites within the Upper Clear Creek watershed indicated that most of the more contaminated sites were outside of the park boundaries, especially at sites within the French Gulch, Cline Gulch, and Whiskey Creek watersheds. The site with the highest overall contamination within the park, based on both fish and invertebrate data, was WLCC, a site on Willow Creek impacted by acid mine drainage and listed as impaired under Section 303(d) of the Clean Water Act.

Compared with other recently evaluated mine-impacted watersheds in northern California, invertebrates, amphibians, and fish from sites within the Upper Clear Creek watershed tended to have significantly lower concentrations of Hg than at most other sites. For other metals and trace elements, Upper Clear Creek sites were only compared with the Deer Creek watershed, Nevada County, California. Copper from both Willow Creek sites (WLCC and WLTH) in the Clear Creek watershed was the only metal with concentrations in biota that were significantly higher than biota from Deer Creek