It was hard enough to find the hippo, a massive, ornery male with a reputation for harassing local ranchers. For three long months, the scientists tracked it through the Colombian countryside, staking out lakes, traipsing through brush and camping on nearby farms.

But castrating it — that was an almost herculean task. They had to inject it with a potent elephant tranquilizer before it was safe to approach. Even with the hippo immobilized, it was surprisingly difficult to locate his, ahem, parts.

“It was horrible,” recalled David Echeverri Lopez, a researcher at the regional environmental agency Cornare who led the 2013 sterilization effort. “You cannot just go on the Internet and Google, ‘What to do with a hippopotamus?’”

After all, the creature belonged on the other side of the ocean, in the savannas and forests of sub-Saharan Africa. But in the 1980s, drug kingpin Pablo Escobar smuggled four hippos onto his private country estate. Now dozens of its wild spawn roam the wetlands north of Bogota, the largest invasive species on the planet.

Locals see the hippos as an unofficial mascot. But to scientists, they are an ecological menace, competing with native wildlife and polluting local waterways. Occasionally, they have even attacked humans.

Now a study forecasts that the invasive hippo population will swell to almost 1,500 individuals by 2040. At that point, their environmental impacts will be irreversible and their numbers impossible to control. Something needs to be done — and soon.

In the beginning, there were only four hippos. How much trouble could they cause? So reasoned Colombian officials charged with dismantling Escobar’s sprawling country estate after his death in 1993. They were reluctant to approach the animals, each highly aggressive and roughly the size and weight of a four-door sedan. While most of the drug lord’s exotic animals were sent to zoos, the hippos — three females and one male — were allowed to roam.