The aim of this research was to determine the effect of a cage farm with a capacity of about 55 t on the benthic macrofauna in Kesikkopru Dam Lake. At 3 stations (the cage and 15 m and 60 m from the cage) selected for this purpose the abundance and composition of benthic macrofauna were determined for 11 months. The abundance of benthic macrofauna (individuals/m(2)) between the stations was statistically significant (P < 0.05). The abundance of benthic macrofauna was higher at the cage station than at the other 2 stations, except in April and November. During the research period the lowest number of individuals (937 individuals/m(2)) was found at the second station 15 m from the cage in February; and the highest number (14,091 individuals/m(2)) was determined at the cage station in December. Members of the class Pelecypoda were found at all 3 stations. Dreissena, which is a member of the class Pelecypoda, was the most dominant benthic organism (54%), followed by Chrinomus (30%) and Tubifex (11%). At the cage station, while members of the class Pelecypoda were found, no members of the classes Insecta, Oligocheta or Crustacea were found. The highest number of benthic macrofauna genera (7) was found at the station 60 m from the cage in April and November. The lowest number of genera (1) was found at the cage station in July. The results of this study in Kesikkopru Dam Lake reveal that the cage culture has a localizing effect on the abundance and composition of benthic macrofauna.