This research used a weight-of-evidence approach to quantify effects of polycyclic aromatic hydrocarbons (PAHs) on benthic communities at Isle Royale National Park, USA. We compared PAH concentrations in sediment, sediment toxicity, and benthic community structure at reference sites and PAH-contaminated sites located adjacent to several marinas. Analysis of PAH profiles indicated that all marina locations were influenced by pyrogenic compounds, demonstrating anthropogenic sources of contamination. Although levels of total PAHs in sediment were significantly elevated at marinas, these concentrations were only slightly greater than the threshold effect concentration (161 µg PAH·g^-1 TOC). Survival of the amphipod Hyalella azteca in laboratory toxicity tests was negatively correlated with PAH concentration; however, the only significant difference in survival between controls and marina sediments was observed at the most contaminated site. Abundance of the PAH-sensitive amphipod Diporeia spp. was significantly lower at marina sites compared to reference sites. Increased PAH concentration, decreased survival of H. azteca, and reduced abundance of Diporeia spp. at the marina sites were consistent with the hypothesis that PAHs impacted these areas. Because PAH contamination was relatively low, a weight-of-evidence approach was essential for distinguishing moderately impacted sites from reference sites.