Apparently sterile lesions developed in the skin and musculature of channel catfish (Ictalurus punctatus) six days after fish were severely stressed by an oxygen depletion associated with a phytoplankton die-off in an 8.9 ha pond. Lesions were characterized by hemorrhage and necrosis. Aeromonas hydrophila was isolated from either the lesions or internal organs of all moribund fish necropsied the day after lesions were first found. As the water quality improved the health of the fish improved. Water quality data collected before and after the oxygen depletion, and associated fish mortality, are presented.