Colombia is to cull some of the 166 hippos descended from a herd owned by drug lord Pablo Escobar in the 1980s.
Environment Minister Susana Muhamad said that 20 would be sterilised, others would be transferred abroad – and “some” would be euthanised.
Experts have for years tried to control the hippo numbers.
Escobar imported the animals for his private zoo at Hacienda Nápoles. They were left to roam after he was killed in a shootout with police in 1993.
Authorities have tried various approaches to curb the population explosion in Colombia’s main river, the Magdalena, including sterilisation and transferring individuals to zoos abroad.
Efforts failed to contain the herd’s growth, however, with a lack of predators and the fertile and swampy Antioquia region providing perfect conditions for the native African animal to thrive.
Their fate was sealed when hippos were declared an invasive species last year, opening the door to a cull.
“We are working on the protocol for the export of the animals,” Ms Muhamad was quoted as saying by local media.
“We are not going to export a single animal if there is no authorisation from the environmental authority of the other country.”
She said the ministry was creating a protocol for euthanasia as a last resort.
Colombian experts have long warned that the hippos’ uncontrolled reproduction poses a threat to humans and native wildlife.
Estimates suggest that the population could reach 1,000 by 2035 if nothing is done, but animal activists say sterilization entails suffering for the animals – and great danger for the vets doing it.
The hippo is one of the largest land animals, with adult males weighing up to three tonnes. They are also among the most dangerous, killing around 500 people a year.
Fishing communities along the Magdalena River have come under attack and some hippos invaded a school yard, although no one has been killed.
Escobar was the head of the Medellín cartel and dubbed the “cocaine king” who amassed an estimated $30bn (£25bn) fortune smuggling drugs into Miami and the southern United States.
His reign of terror spanned more than a decade and involved kidnappings, hundreds of murders, bribery, bombings and turf wars with rival drug barons – as well as a brief sojourn as an elected politician.
As one of the most-wanted men on the planet, he gave himself up to Colombian authorities in 1991 on agreement that he would spend five years in a prison he had built, known as La Catedral.
Escobar went on the run a year later amid government attempts to move him to a more secure jail.
With a $2m US bounty on his head, he met his end in his home town of Rionegro – he was shot dead on a rooftop on 2 December 1993 as he tried to evade police.
He left a legacy of violence but also the 5,500-acre Hacienda Nápoles, private citadel in Antioquia containing, among other things, a menagerie of four hippos, plus giraffes, camels and zebras.
The hacienda was given over to poor locals by the government after Escobar’s death, and the hippos were left to roam free as they were deemed too difficult to seize.