The feeding ecology of the translocated marine fish sand smelt Atherina boyeri was studied in Hirfanli Reservoir, a freshwater dam lake located in Central Anatolia. The data revealed that the sand smelt fed mainly on larger zooplankton, such as adult copepods and cladocerans. Fish eggs and juvenile fish were also found in the stomach content. There was a considerable dietary overlap among size groups larger than 30 mm total length. Larger individuals have also cannibalistic behaviour as they consumed juveniles of sand smelt. The proportion of empty stomachs was maximum in winter and minimum in summer. The trophic niche breadth was the highest in summer. The results suggested that the sand smelt may have a remarkable impact on zooplankton communities in the Hirfanli Reservoir.