The studies included 10 public indoor swimming pools and 3 public open-air swimming pools located in the city of Szczecin. In 2003, water samples were collected for detection of virulent amphizoic amoebae strains. In all pools, 16 strains of thermophilic Acanthamoeba spp. were isolated, 5 of which proved virulent for mice. No pathogenic strains were detected in the water sampled in the indoor swimming pools, and the virulent strains, AD 16, AD 148, AD 166, AM 17, and AM 148, were found only in the open-air swimming pools. The post-mortem studies of mice that had been inoculated with these strains revealed the amoebae invasions in brain, lungs, liver, kidneys, and spleen.