Hyporheic zone is a dynamic active ecotone of the sub-surface area that provides habitat for larvae of aquatic insects. This study examined the food web in the hyporheic zone by determining major basal resources for and trophic position of invertebrates, and also examined whether adult insects can serve as a proxy of pollution effects in a gravel bed river in Hokkaido, Japan, where a longitudinal nutrient gradient existed because of a point source. Stable nitrogen and carbon isotope ratios (SIRs) were used to determine the effects of water pollution and major basal carbon sources, respectively. Hyporheic Alloperla ishikariana larvae (Order: Plecoptera, Family: Chloroperlidae) were consistent in terms of their trophic position as primary consumers. Similar water quality both in hyporheic and surface water suggested high hydrological exchanges and resulted in positive increases of nitrogen SIRs of Alloperla ishikariana larvae in proportion to nitrate level in surface water. Furthermore, nitrogen SIRs of Alloperla ishikariana larvae were highly correlated with those of their adults (R²=0.86) indicating that adults can provide information on the spatial variability of nitrogen SIRs in the hyporheic zone. Overall, adult aquatic insects can be used as an indirect and useful indicator of water pollution in hyporheic food web.