Freshwater gastropods represent common and important members of aquatic ecosystems, but emerging chemical contaminants may challenge gastropod fitness. As the use of nanosilver (n-Ag) increases, the potentially adverse effects of n-Ag on aquatic ecosystems remain largely unknown. In aquatic ecosystems, we hypothesized that n-Ag at trace concentrations may affect the ability of organisms to sense predation by interfering with chemoreception. We performed a microcosm experiment to assess the freshwater gastropod, Physa acuta, to detect and respond to natural predator cue derived from pumpkinseed sunfish (Lepomis gibbosus), at environmentally relevant nominal n-Ag concentrations over 24 h. For the first 6 h exposure, gastropod predator avoidance behavior measured 30–47% less in treatments with environmentally relevant n-Ag concentrations compared to treatments without n-Ag. Regardless of predator cue presence or absence, the proportion of gastropods occupying near surface habitat in 30 µg/liter n-Ag appeared 20–26% greater relative to no n-Ag treatments for the first six exposure hours, indicating contaminant avoidance behavior. These results suggest that nonlethal concentrations of emerging contaminants affect animal behaviors. These behaviors, in turn, may have consequences for species interactions and ecosystems. Thus, future research efforts need to address the ecology in ecotoxicology by understanding how environmentally relevant concentrations of emerging contaminants may adversely affect the chemoreception, growth, and fecundity of organisms essential to the structure and function of freshwater ecosystems.