Freshwater mussel populations and distributions have declined over the past several decades in the Buffalo River, Arkansas. Among many possible causes, this study tested the hypothesisthat ammonia concentrations in parafluvial flows through gravel bars might be high enough to impair the survival and growth of juvenile mussels. Ammonia, pH, temperature, and dissolved oxygen were measured in interstitial and water column samples from gravel bars to test for possible longitudinal gradients. Samples were taken along 3 large bars at locations within the Buffalo National River, at approximate bi-weekly intervals between June and September of 2010. Water sample ammonia concentrations were compared with revised US Environmental Protection Agency water quality criteria for the protection of aquatic life. In addition, juvenile mussels were caged immediately upstream and downstream at each of the monitoring sites to test for site and location differences in growth and survival. Interstitial DO, temperature, and pH decreased, and ammonia concentrations increased, as water traveled downstream through the gravel bars. During drought periods when the river was at its lowest flow, ammonia concentrations at some sites exceeded levels that have negative effects on mussels in laboratory tests. However, growth of caged mussels was generally strong at both upstream and downstream locations. Growth rate rose as the river warmed during May and June, peaked at 26-27°C in July, and was lower when temperatures exceeded 28-30°C in both May and August-September. Results indicate that while ammonia concentrations increase in parafluvial flows along bars, these concentrations are diluted rapidly in surface waters and may not have significant impacts on local mussel populations.