Naegleria fowleri /nəˈɡlɪəriə/ is a free-living excavate form of protist typically found in warm bodies of fresh water, such as ponds, lakes, rivers, and hot springs. It is also found in soil, near warm-water discharges of industrial plants, and unchlorinated or poorly chlorinated swimming pools in an amoeboid or temporary flagellate stage. There is no evidence of this organism living in salt water. It is an amoeba belonging to the groups Percolozoa or Heterolobosea.
N. fowleri can invade and attack the human nervous system. Although this occurs rarely, such an infection nearly always results in the death of the victim. The case fatality rate is estimated at 98%