Naegleria fowleri

Naegleria fowleri is a free-living form of protist typically found in warm fresh water, from 25–35 degrees Celsius. It belongs to a group called the Percolozoa or Heterolobosea.
"N. fowleri" can invade and attack the human nervous system; although this occurs rarely, such an infection will nearly always result in the death of the victim.