In this study, fish's morphologic and anatomic lesions caused by motile aeromonad septicemia (MAS) depending on environmental stress in carp, Cyprinus carpio population living in Lake Todurge were identified. Various morphological and anatomical deformations and lesions were observed in the body of approximately 17% (252 fish specimens) of a total of 1488 carp samples. Bacteria are grown from all wipe samples. Bacterial colonies have a gray-white appearance with round, convex and smooth edges. 15-20 cfu colonies were observed in each aerop culture. As a result of analysis of wet wipe samples from infected fish's skin, gill, kidney and liver, it is determined that the bacteria which causes septicemia is Aeromonas sobria from the Aeromonadaceae family (with 99.2% confidence value). No bacteria were grown in cultures except A. sobria. Some symptoms of the infection are inflammation on different parts of the fish bodies, eruption on skin and scales, dermal necrosis, degeneration at soft rays of the fins, exophthalmos, and purulent liquid accumulation in the abdominal cavity, etc. Infected fish were most commonly encountered in July and August (water temperature above 20 degrees C), the lowest in October and November (water temperature below 10 degrees C).