An ocean away from their kindred in Africa, a group of invasive hippos roaming the Colombian wild has garnered quite the controversial reputation. The river-dwelling mammals don’t exactly belong in this environment, yet an estimated 91 of them currently inhabit the Magdalena River basin in Colombia.

As the hippo’s numbers burgeon, the scramble to curtail population growth has reached a boiling point. The consequences that have arisen from the hippos’ presence, scientists warn, will only amplify if the animals aren’t dealt with swiftly. 

But how did these hippos get there in the first place, and why do they have scientists worried?

How Many Hippos are in Colombia?

A 2023 paper published in Scientific Reports estimates that there are 91 hippos currently in the Magdalena River basin and that the population is growing at a rate of 9.6 percent per year. At this rate, there will be 230 hippos by 2032 and over 1,000 by 2050. 

The hippos have impacted the local ecosystem by moving more organic terrestrial matter to aquatic environments. The increased nutrients that they bring by grazing on grass and then excreting in water fertilizes the lakes and rivers, which may lead to eutrophication — caused by an excess of nutrients and associated with harmful algal blooms. 

People who live in nearby agricultural villages, and especially those who access the Magdalena River, could be exposed to danger from the hippos. According to the paper, two people have been attacked and injured by the hippos since 2019. The threats that humans and wildlife face will likely escalate in the future, depending on how the population is managed. 

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A Drug Lord’s Zoo

The first hippos in Colombia — 3 females and 1 male — came at the behest of drug lord Pablo Escobar, who imported them in 1981 from a U.S. zoo. They became a feature of Escobar’s own private zoo at his sprawling estate, Hacienda Nápoles. 

The zoo shut down in 1993 after Escobar’s death, but the hippos remained on site due to challenges transporting them. In the coming years, they reproduced and made the surrounding landscape their home. From 1993 to 2009, 4 hippos turned into 28. 

The initial solution to stop the hippos’ growth was culling, or killing for population control. But when authorities culled a male hippo in 2009, a fierce reaction from animal rights activists followed. Ever since a judicial ruling banned the shooting of hippos, authorities have struggled to commit to alternative methods. 

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What Will Happen To The Hippos? 

The answer to the hippo problem has encountered various obstacles in recent years, including cost and public reaction. Scientists have suggested immediate action rather than further delay, as explained in the Scientific Reports paper. However, debate over the available methods rages on.

Male sterilization would be the most cost-effective method right now, especially if all males are sterilized in one year. If authorities choose instead to only sterilize a few males per year, it could take up to 50 years or more for the population to entirely disappear. 

Contraceptive methods via oral-based feed or darts would also take decades to complete. Eliminating the population through this method would take 45 years of consecutive treatment. 

Veterinary-assisted euthanasia would greatly speed up the process, though it might incite stronger public outcry. Every hippo could theoretically be euthanized in a single year.

It will take deliberate consideration by authorities to choose the path forward, but the paper’s authors say that delaying for too long could create a bigger impact as the hippo population grows. 

If the population control process doesn’t start soon, the hippos will likely expand into other territories. The ecological impacts and the potential for conflict with humans could enter new levels of severity in the future as a result. Regardless of what option is chosen, it seems that this critical moment has already spawned serious repercussions as the invasive hippos continue to proliferate. 

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