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There’s surviving, and then there’s thriving in a literal sewer. A colony of guppies—the same tiny tropical fish people keep in desktop aquariums—has managed to do both for more than 40 years in the waste-choked canals of a Kyiv treatment plant.

Guppies are a very hardy fish, I heard they live in rivers of Southern Europe where the winters are mild and the water doesn’t freeze.

Unfortunately, the guppies’ reign is under threat. In recent years, their numbers have declined due to an invasive predator known as the rotan-head (Perccottus glenii), a fish that wandered in and started eating them. Even in the sewers, nothing gold can stay.

This second fish is also an invasive species from Eastern Asia. Species tend to be introduced to places by natural means, some species tend to migrate around the World quite naturally but often this introduction is the work of humans.