Aquatic-terrestrial contaminant transport via emerging aquatic insects has been studied across contaminant classes and aquatic ecosystems, but few studies have quantified the magnitude of these insect-mediated contaminant fluxes, limiting our understanding of their drivers. Using a recent conceptual model, we identified watershed mining extent, settling ponds, and network position as potential drivers of selenium (Se) fluxes from a mountaintop coal mining-impacted river network. Mining extent drove insect Se concentration (p = 0.008, R²  = 0.406), but ponding and network position were the principal drivers of Se flux through their impact on insect production. Se fluxes were 18 times higher from ponded, mined tributaries than from unponded ones and were comparable to fluxes from larger, productive mainstem sites. Thus, contaminant fluxes were highest in the river mainstem or below ponds, indicating that without considering controls on insect production, contaminant fluxes and their associated risks for predators like birds and bats can be misestimated.