After months of hesitation, Colombian authorities have declared late drug lord Pablo Escobar's famous hippos an "invasive species".

Killing them is also considered a “necessary option” in the statement from the Ministry of the Environment, which is based on a study by the Alexander von Humboldt Institute in Bogotá and the Institute of Natural Sciences at the National University in the Colombian capital.

This means that the approximately 130 hippos that roam free north of Bogotá near the Magdalena River face an uncertain future.

They are descended from the few specimens that Escobar had flown in for his private zoo at the Hacienda Napoles estate.

Authorities say the originally sub-Saharan grass-eating giants are threatening local wildlife and people living along the river.

Since the sterilization of the animals, which can weigh up to 1.8 tons, is expensive and difficult, "culling remains an option on the table," says David Echeverri, head of the regional environmental agency Cornare, which is responsible for sterilization.

"It might be the only way to prevent the problem from getting worse."

Escobar built the infamous Medellín drug cartel, becoming one of the richest men in the world, according to Forbes.

Among other things, he afforded a private zoo with hippos, flamingos, giraffes, zebras and kangaroos.

In 1993 Escobar was shot dead by the police, after which all the animals were sold to zoos - except for the hippos.

The water-loving animals stayed on Escobar's estate and multiplied.

They are now probably the largest hippopotamus population outside of Africa.

The animals have long been a headache for the authorities, and according to studies, the colony could quadruple in ten years.

At the same time, a loud campaign for their protection was formed.

Although the details of the authorities' new plan to manage the population are not yet known, former Environment Minister Manuel Rodríguez urged the government to also consider hunting the animals: "Of course there are animal rights activists who are against it, but what is it Alternative?" suggests Rodríguez, who collaborated on the study on the impact of the hippo invasion.

So far, Cornare has only managed to sterilize 11 hippos and administer contraceptives with a dart to 40 others.

That cost the equivalent of more than 87,000 euros, but could not stop the multiplication.

"Everything to do with hippos is complex, expensive and dangerous," says Echeverri.

"For every operation performed, ten animals are born."

Rodríguez warns of a threat to fishermen and other shore residents.

In 2021, Cornare reported two hippopotamus attacks on humans, both of which escaped with injuries.

In Africa, hippos kill hundreds of people every year.

"We could see tragedy," Rodríguez warns.

The hippos also threaten the manatees — large mammals native to the Magdalena River — and a variety of native fish.

Earlier this year, activists, supported by Green parliamentary candidate Luis Domingo Gómez, proposed creating a hippo sanctuary using public and private funds.

But experts dismiss the proposal as too costly and no less damaging to the ecosystem.

"Do we want to maintain a sanctuary for hippos, which threaten manatees?" Rodríguez asks. Biologist Nataly Castelblanco, an expert on manatees, shares his concerns. She recently tweeted, "Native species take precedence over invasive species."