There is a medical textbook called "Parasitic Diseases, 7th Edition" you can get the .pdf free and legally from
https://parasiteswithoutborders.com/books/
Below is several small excerpts on the brain eating amoebae you are likely thinking about.
Naegleria fowleri Pronunciation: \nā-ˈglir-ē-ə\ N. fowleri, commonly known as the braineating amoeba, is a robust thermophilic free-living amoeba found around the world in warm freshwater.105 It thrives in standing freshwater environments such as hot springs, heated swimming pools, and hot tubs.
N. fowleri causes a serious, often fatal, fulminating infection of the CNS, referred to as primary amoebic meningoencephalitis (PAM).107, 108 Cases of PAM have occurred in the United States, Europe, Australia, South and Central America, and Southeast Asia. The infection is typically acquired by swimming or bathing in water above 37 °C. It is presumed that this unusual environment results in the selection of an abundance of thermally-tolerant organisms, including N. fowleri. 109 Diving or playful splashing activity can force heated water containing the trophozoites up into the nose and through the cribriform plate. N. fowleri invades and migrates along the base of the brain, and then penetrates deeply into the cortex producing an acute inflammatory reaction with extensive areas of lysis. Amoebae lyse their way through tissue, probably aided by a poreforming protein similar to that of Entamoeba histolytica. 110 Symptoms include severe frontal headache, vomiting, confusion, fever and coma, followed by death.111
Amphotericin B was the initial therapeutic agent used to treat patients, but mortality remained greater than 95% despite administration.115
N. fowleri is ubiquitous in distribution. One study conducted in Oklahoma showed that the number of pathogenic free-living amoeba species varied throughout the seasons and were most prevalent in natural water sources (i.e., lakes and impoundments) in the spring and fall. This suggests that the organisms are normally found in benthic zones (the lowest levels of water), and only gain access to the water column during periods of lake “turn over.”118 There are certain behaviors such as the use of neti pots and religious ablutions where warm water, potentially containing these amoebae, is forced up the nose. Modifications of these behaviors or only using water that does not contain these amoebae could reduce infection risk.
Due to the rarity of this disease, most situations leading to infection must be classified as incidents of unlucky circumstance, especially when one considers the number of visits to hot tubs, spas and natural hot springs, and the number of user hours spent relaxing in them.