In addition to the original
habitat of the
guppy (see write-up above, from
Percepied) and the aquarium, guppies (and to a lesser extend
neon tetras) also can be found in
rivers and
canals near
thermal power plants in Europe, but I assume in other areas around the globe with a
moderate climate too.
The used water of the
power plant disposed in the rivers is consistently a few
degrees higher than the normal water
temperature, providing a acceptable
environment for the guppies not only to survive, but
adapting themselves to the new situation to
breed and
flourish.
The guppies can get there because of the people who don’t want the guppies in the
aquarium anymore, or just some but not all: they flush them through the
toilet.
My dad was one of those persons who did that too, “giving them back their freedom” he called it...