Colombia India Trinidad Russia 
Answer: Colombia
Hippopotamuses are native to Africa, but there isn’t anything specific to the mid-to-south African range they call home that restricts them from living elsewhere (outside of the inherent improbability of surviving a migration through northern Africa and the Middle East to get to another hospitable home range). In fact, courtesy of a notorious 1980s Colombian drug kingpin, we now know that hippopotamuses are perfectly happy in South America.
In the 1980s, Pablo Escobar was the world’s wealthiest drug kingpin and his cocaine empire provided him with so much cash he could effectively spend it all day, hand over fist, and still have warehouses (literally) full of cash left over. He built enormous homes, had golden guns, and even set up his own zoo on the grounds of his primary compound Hacienda Napoles, a sprawling estate located outside of Medellin, Colombia.
The zoo included elephants, antelopes, giraffes, ostriches, and, among other exotic animals, the hippopotamuses this story revolves around. When his drug empire collapsed in the early 1990s, it was fairly easy for authorities to catalog and distribute his assets; the zoo, however, proved to be rather difficult to handle. Birds and more cooperative animals like the antelope and elephants were moved to national zoos. The hippopotamuses though were quite aggressive and the authorities opted to scrap the plans to move them and simply left them on the estate.
The animals eventually broke free from the abandoned estate, began breeding, and took to the nearby Magdalena River. Between their escape and the present, the population has multiplied and Columbia now has the distinction of being the only country with an invasive herd of hippopotamuses.
Image by Paul Maritz.