Abstract Larger fish species may not always be suitable for monitoring the response to industrial effluents because they are mobile and capable of extensive movement beyond effluent exposure areas. Spoonhead sculpin (Cottus ricei) was collected upstream and downstream of a large bleached-kraft pulp mill on the Athabasca River, Alberta, Canada, during fall and spring periods to determine whether small, sedentary fish species demonstrate responses reflecting local exposure conditions. During the fall sampling period, exposed fish were older and larger than upstream fish and showed increases in condition, gonad size, egg weight, liver weight, and hepatic mixed function oxygenase activity (7-ethoxyresorufin O-deethylase [EROD]). Sculpin collected from the opposite river bank, where exposure was reduced, showed condition factors, gonad size, egg weight, liver weight, and EROD activity that were not significantly different from reference sites or intermediate between reference and downstream values. In the spring after a prolonged overwinter exposure to higher effluent concentrations, exposed fish were larger, showed increased size-at-age, condition, liver weight, ovary size, and EROD activity. Far-field collections showed that most responses persisted downstream for at least 48 km. The general response of exposed spoonhead sculpin was consistent with a nutrient enrichment effect described in studies investigating water quality, algal growth, and benthos communities at this site but also may be related to reduced competition associated with the loss of older fish observed in the spring. The use of small species for sentinel monitoring provided a viable alternative to use of larger, more mobile species.