Hippos wallow at a lagoon in the Hacienda Napoles Park, once the private estate of drug kingpin Pablo Escobar, in Puerto Triunfo, Colombia. Fernando Vergara/AP hide caption

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Fernando Vergara/AP

DORADAL, Colombia—In a small town in central Colombia, the grunt of hippos has become part of the soundscape.

Every afternoon in Doradal, locals and tourists gather at a lake on the edge of town. They chat and drink beers as they watch the giant beasts floating in the water.

"This is one of the main attractions in town," says Lina Morales, a local hotel worker.

But this group of hippos—the only wild herd outside Africa—has also become a threat to people and the local environment, scientists argue.

A recent proposal by Colombia's government to cull the animals has sparked a new debate in the nation's decades-long hippo saga.…