Naegleria fowleri infects people by entering the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. In very rare instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or heated tap water < 47°C) enters the nose. Once the amoeba enters the brain, it causes a usually fatal infection called primary amoebic meningoencephalitis (PAM).  Naegleria are also notable because some species change their form based on the chemistry of their surroundings, transitioning from an immobile cell to a flagellated cell.