ELISA and Southern blots techniques were employed to detect the pathogenic amoeba Naegleria fowleri in river water used for cooling by a French power plant. Water samples from 100 ml to 1 ml, collected at two sites, were filtered. After incubation of the filters at 44°C for 48 h, 21 Naegleria strains were removed. 4 of those strains were identified as N. fowleri by both ELISA and DNA probe, showing the good correlation between these techniques applied to environmental samples.