Riparian spiders are being used increasingly to track spatial patterns of contaminants in and fluxing from aquatic ecosystems. However, our understanding of the circumstances under which spiders are effective sentinels of aquatic pollution is limited. Here we test the hypothesis that riparian spiders may be effectively used to track spatial patterns of sediment pollution by polychlorinated biphenyls (PCBs) in aquatic ecosystems with high habitat heterogeneity. We found that spatial pattern of ΣPCB concentrations in two common families of riparian spiders sampled in 2011-2013 generally tracked spatial variation in sediment ΣPCBs across all sites within the Manistique River Great Lakes Area of Concern (AOC), a rivermouth ecosystem located on the south shore of the Upper Peninsula, Manistique, MI, that includes harbor, river, backwater, and lake habitats. TOC-normalized sediment ΣPCB concentrations explained 41% of the variation in lipid-normalized spider ΣPCB concentrations across 11 sites. Furthermore, two common riparian spider taxa (Araneidae and Tetragnathidae) were highly correlated (r(2) > 0.78) and had similar mean ΣPCB concentrations when averaged across all years. Our results indicate that riparian spiders may be useful sentinels of relative PCB availability to aquatic and riparian food webs in heterogeneous aquatic ecosystems like rivermouths where habitat and contaminant variability may make using aquatic taxa less effective. Furthermore, our approach appears robust to heterogeneity in shoreline development and riparian vegetation that support different families of large web-building spiders. This article is protected by copyright. All rights reserved.