The Western Airborne Contaminants Assessment Project (WACAP) was initiated to determine the risk to ecosystems and food webs in western national parks from the long-range transport of airborne contaminants. It was designed and implemented by the National Park Service's Air Resources Division in cooperation with many western national parks, the Environmental Protection Agency, the US Geological Survey, the US Forest Service, Oregon State University, and University of Washington. The project objectives were: Determine if contaminants are present in western national parks; If present, determine where contaminants are accumulating (geographically and by elevation); If present, determine which contaminants pose a potential ecological threat; Determine which indicators appear to be the most useful to address contamination; and Determine the sources for contaminants measured at the national park sites.