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But their proliferation — they are now the largest herd of hippos outside of Africa, with an estimated 35 members — could cause a problem for such native wildlife as otters and manatees. “If they get aggressive, they pose a risk to Colombian biodiversity,” said biologist David Echeverri Lopez.

Yet Colombia is at a loss of how to handle them. Local people have grown fond of the animals — despite them being the most dangerous creature in Africa, they have yet to kill a Colombian.

Two years ago the country was amazed by a photo of a small girl in a village sitting on the floor, with a seemingly tame hippo lying on the floor next to her. Later that year another girl told a local newspaper she kept one as a pet. “My father brought a little one home once,” she said. “I called him Luna (Moon) because he was very sweet — we fed him with just milk.”

Another child, a boy, told the paper: “My father has captured three. We bottle-feed them because they only drink milk. They have a very slippery skin.” In 2009 one of the hippos, Pepe, was tracked down and shot. Animal rights activists unleashed a storm of condemnation, as well as a flash mob of 100 hippo-masked protesters in Bogota.

Authorities have also tried to capture and castrate the animals, and call in Africa-based hippo experts, to little avail.

Echeverri and Leon, the vet, are building barriers of rocks, trees and wire to keep the hippos from roaming too far, and growing fodder to keep them happy where they are.

The wandering hippos have been sighted up to 160 kilometres away. “It has become normal to see them around here,” said Clara Nunez, 48. “It’s like being in Africa. It is a privilege.”

She added: “But when one gets close, it is a bit scary.”