Naegleria fowleri, often called the 'brain-eating amoeba,' is a single-celled organism found in warm freshwater environments like lakes and hot springs. It's microscopic, thermophilic, and primarily feeds on bacteria. Its pathogenic nature comes to light when it enters the human body through the nose, causing a rare but often fatal brain infection.

Naegleria fowleri is found in warm freshwater environments worldwide, predominantly in regions with a warm climate. It is commonly reported in the United States, particularly in the southern states, but also occurs in other parts of North and South America, southern Europe, Africa, Asia, and Australia.

This species thrives in warm freshwater such as lakes, rivers, hot springs, and poorly maintained or untreated swimming pools. The optimal temperature range for Naegleria fowleri is between 25°C and 35°C (77°F and 95°F), but it can survive in water temperatures up to 45°C (113°F).

Naegleria fowleri is a free-living amoeba that exists in both trophozoite and cyst stages. It feeds on bacteria and other microbes in the water. Under unfavorable conditions, such as cold temperatures or lack of food, it can form a resistant cyst to survive. The amoeba is not typically pathogenic but can cause primary amoebic meningoencephalitis (PAM) in humans if contaminated water enters the nasal passages.