Mercury, originating from abandoned mercury mines and thermal springs in the Cache Creek Watershed and transported to the San Francisco Bay and Delta, especially during flood events, is the focus of this work. Documentation of mercury levels in biota and identification of point sources of bioavailable mercury in the Cache Creek watershed are necessary to identify and rank potential remediation sites. These baseline data can then be compared with post-remediation data to assess the effectiveness of cleanup efforts. Another benefit from the study will be the evaluation of the adverse effects that mercury may have on fish, amphibians, and swallows. By collecting samples from different trophic levels, we will be able to evaluate accumulation pathways for mercury in the Cache Creek food web. This will facilitate risk determinations for threatened species and species of special concern within the watershed. Finally, mercury accumulations in swallow eggs and amphibians will suggest the applicability of their use in biomonitoring for mercury in other areas, and our assessment of genetic damage in amphibians may reveal a non-lethal biomarker useful for identifying mercury exposures across broader geographical regions of California. This is a two-year study conducted jointly by the Davis Field Station of the Biological Resources Division of U.S. Geological Survey and the Environmental Contaminants Division of the Sacramento Field Office of the U.S. Fish and Wildlife Service.