A wild herd of hippopotamuses that once belonged to a Colombian drug lord are now spreading across the countryside and no one knows what to do with them.

Situated halfway between the city of Medellin and Bogota, the Colombian capital, Hacienda Napoles was the vast ranch owned by the drugs baron Pablo Escobar. In the early 1980s, after Escobar had become rich but before he had started the campaign of assassinations and bombings that was to almost tear Colombia apart, he built himself a zoo.

He smuggled in elephants, giraffes and other exotic animals, among them four hippos – three females and one male. And with a typically grand gesture, he allowed the public to wander freely around the zoo. Buses filled with schoolchildren passed under a replica of the propeller plane that carried Escobar’s first US-bound shipments of cocaine. While Don Pablo masterminded the operations of the Medellin Cartel from his villa on the hill, the locals gazed at the strange animals and even stranger concrete dinosaurs that Escobar built for his son.

When Hacienda Napoles was confiscated in the early 1990s, Escobar’s menagerie was dispersed to zoos around the country. But not the hippos. For about two decades, they have wallowed in their soupy lake, watching the 20sq km (8 sq mile) park around them become neglected and overgrown – and then transformed back into a zoo and theme park, complete with water slides. All the while, the hippos themselves thrived, and multiplied.

The hippos also escaped from the zoo, and because the environmental conditions in Colombia are ideal for these invasive hippos, they are prospering wherever they go.