In the 1980's, Colombian drug lord Pablo Escobar decided to bring four hippos (one male, three female) to Colombia to become part of his private zoo. Because, you know, as a drug lord, it's pretty imperative to your status to have your own zoo.
However, after Escobar's death twenty years ago, the majority of the zoo animals were dispersed to various other zoos and sanctuaries. The hippos, however, remained in their lake at the zoo, and the property eventually became overgrown. The hippos more or less adopted the surrounding environment as their own.