The feeding habits of perch (Perca fluviatilis) were documented by analyzing gut contents of more than 3300 specimens collected seasonally at nine stations located along the impounded large river in Turkey. Perch largely preferred fish (36%), insects (54%), other crustaceans (16%) and daphnia (13%). Spatial analysis showed that perch substantially preferred fish in the river section above the dam lakes and insects, crustacean and fish in the river section below the dam lake and in dam lakes. The perch at every size seemed to prefer fish with the highest and lowest percentage obtained for 0 to 80 and 141 to 200 mm. Insects and crustaceans were important for 81 to 140 mm and 0 to 120 mm length, respectively. Crustaceans were important in June, November and July. Insects and fish except for June 2009 constituted an important portion of the diets during every sampling month. The perch showed a piscivory feeding habit, a result obtained by trophic level calculated by stomach contents (3.87) and stable isotope (3.91) methods. Trophic level change little during the ontogeny with relatively higher value obtained for the larger length. The perch inhabiting in the river section above the dam lakes had the highest trophic level compared to the other sites. Diet breadth of perch was lower and higher for larger and middle length (101 to 140 mm), respectively. The diet breadth was higher in dam lakes, indicating opportunistic feeding habits in lakes. Being the most abundant fish species in the study system and showing predatory feeding habits suggested that perch may have an effect on local fish assemblage and itself through predation.