We hypothesized that C. fluminea could remove anthropogenic N at a rate sufficient to affect particulate N in the water column of North Buffalo Creek, North Carolina, USA, a 4^th-order stream that receives treated urban wastewater. We used stable-isotope analysis to evaluate trophic relationships between seston and C. fluminea and conducted field sampling and laboratory experiments to evaluate the potential qualitative and quantitative effects of C. fluminea on seston. Corbicula fluminea δ¹⁵N was 3 to 5‰ enriched compared to seston along a longitudinal transect downstream of the wastewater treatment plant (WWTP), a result consistent with use of seston N. However, seston δ¹³C declined and C. fluminea δ¹³C showed no pattern with distance downstream, a result that was inconsistent with a trophic relationship between seston and C. fluminea. In 2 laboratory experiments designed to measure filter-feeding rate and qualitative effects on seston, seston ash-free dry mass and chlorophyll a data indicated that C. fluminea either was not filtering or was filtering at a rate insufficient to affect seston concentration over the course of the experiments. δ¹⁵N data showed that the sediment was an N source for C. fluminea, but δ¹³C and C∶N data from the same experiments indicated that C. fluminea probably affected seston quality by suspending benthic algae and returning settled algae to the water column. These results illustrate that the food sources for C. fluminea and implications of C. fluminea activity in stream ecosystems should be evaluated more fully.