Over a 4-month period, 450 perches (Perca flavescens) were captured in four lakes of the Eastern Townships, Québec, and examined for the presence of Aeromonas hydrophila, the causative agent of hemorrhagic septicemia. This bacterium was present in 78 perches. One hundred and eight strains of Aeromonas hydrophila were isolated from the heart, liver, and kidneys of those fishes. The study of the water quality of the lakes has shown that there is no positive relation between pollution and the incidence of Aeromonas in the perches studied.