A free-living ameba is a one-celled organism that lives in water and soil around the world.  Although there are several types of free-living ameba that live in the environment, three are known to cause severe disease in people, these belong to the genera Acanthamoeba, Balamuthia, and Naegleria. Acanthamoeba spp. and Balamuthia mandrillaris are free-living amebae capable of causing granulomatous amebic encephalitis (GAE). Non-keratitis Acanthamoeba infections are rare and usually occur in people with weakened immune systems. Balamuthia mandrillaris  can infect anyone at any time of the year especially if water or soil containing the ameba gets into a wound. You also can become infected breathing in dust containing Balamuthia. Naegleria fowleri thrives in warm freshwater including lakes, rivers, and hot springs and is often called “brain-eating ameba”. Naegleria fowleri produces an acute, and usually lethal, central nervous system (CNS) disease called primary amebic meningoencephalitis (PAM). Brain infections caused by Naegleria fowleri usually occur after someone goes swimming or diving in a lake, river, or other fresh water during summer months and infections often happen when it's been hot for long periods, resulting in higher water temperatures and lower water levels. 

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