Studies of contaminant distributions by the Northern River Basins Study (NRBS) revealed high levels of PCBs in fish in the upper Athabasca and in the Wapiti-Smoky rivers, relative to other areas in the basins. In response to recommendations of the NRBS, the purpose of this work was to investigate the source and reasons for the PCB contamination. In co-ordination with other projects under the Northern Rivers Ecosystem Initiative (NREI) on fish, water, and benthos, this project investigated PCBs in river bottom sediments to see if there were spatial or temporal patterns that might identify the source(s) of contamination.