PUERTO TRIUNFO, Colombia -- Alvaro Molina has had his run-ins with the burly bunch of neighbors with disreputable contacts who showed up about a decade ago along the river in front of his house in Colombia's Antioquia province. But he's learned to live with them and says he is worried about a government plan he fears could harm them.
People around Puerto Triunfo have grown accustomed to the herd of hippopotamuses descended from a few that were imported illegally from Africa in the 1980s by flamboyant drug lord Pablo Escobar, whose former ranch is nearby.
Molina, 57, says he supports the hippos even though he is one of the few Colombians to have been attacked by one. He was out fishing one day when he felt a movement beneath his canoe that spilled him into the water.
"The female attacked me once -- the first pair that arrived -- because she had recently given birth," he said.
Within weeks, Colombia's government plans to sign a document declaring the hippos an exotic invasive species, according to Environment Minister Carlos Eduardo Correa. This means coming up with a plan for how to control their population, which has reached 130 and is projected hit 400 in eight years if nothing is done as they flourish in Colombia's rivers.
Correa said many strategies are being discussed but no decisions have been made. Local communities will be consulted about any plan to control the hippos' population, he added.
"They talk of castration, sterilization, taking the life of some hippopotamuses," he said. "What is important is the scientific and technical rigor with which the decisions are made."
Most people interviewed in Puerto Triunfo, some 120 miles from the capital Bogota, say they can get along with the hippos, and many oppose even sterilization -- let alone killing some.
"They make laws from a distance. We live with the hippopotamuses here, and we have never thought of killing them," said Isabel Romero Jerez, a local conservationist. "The hippopotamuses aren't African now; they are Colombians."
Escobar's Hacienda Napoles -- and the hippos -- have become a sort of local tourist attraction in the years since the kingpin was killed by police in 1993. When his ranch was abandoned, the hippos survived and reproduced in local rivers and favorable climatic conditions. They began showing up around Puerto Triunfo a decade ago.
Scientists warn the hippos do not have a natural predator in Colombia and are a potential problem for biodiversity since their feces change the composition of the rivers and could impact the habitat of manatees and capybaras.
An analysis by the Alexander Von Humboldt Biological Resources Research Institute said that climate change and "an increase in equatorial conditions, the ideal climate for the species" could increase the hippopotamus' dispersion across Colombia, potentially "overlapping with the geographic and ecological niches of native species, increasing the risk of possible competition for resources."
Hippopotamuses can also cause damage to crops because they are mainly herbivores and seek food in large quantities at night.
While hippos are considered one of the most dangerous animals for humans in Africa, there have been only a few injuries recorded so far in these parts.
"I don't consider them a threat, but there are difficulties with them. In the municipality, we have had reports of three attacks on the civilian population," said Carmen Montano, an official with Puerto Triunfo's Municipal Agricultural Technical Assistance Unit.
Locals say the hippos sometimes come out of the water and walk through the streets of the town. When that happens, traffic stops and people keep out of their way.
"The human animal is the one that invades their territory; that is why they feel threatened and attack," said Romero Jerez. "Human beings should be prudent, respectful and keep their distance."
Scientists warn that hippos are territorial and weigh up to three tons.
Daniel Cadena, a biologist and dean of sciences at the Universidad de Los Andes, said they are aggressive animals and not as gentle as people imagine.
"There are estimates in Africa that hippos kill more people each year than lions, hyenas and crocodiles combined," he said.
When the document declaring them an invasive species in Colombia is signed, hippopotamuses will join species such as the giant African snail, coqui frog, black tilapia and lionfish. The declaration will allow the government to allocate resources to control the hippo population, one of the main obstacles.
There is currently an experimental program of immuno-castration with a drug donated by the United States. Surgically sterilizing them requires sedating them, transporting them to a safe place and cutting through their thick skin.
"Hippopotamuses do not have what is called obvious sexual dimorphism; it is difficult to know if an animal is male ... the genitals are internal," Cadena said.
Any population control process promises to be costly and complex because it requires finding the hippos scattered along the mighty Magdalena River.