This article comes from the Bent Fishing Podcast’s “Fish News” segment, where hosts Joe Cermele and Miles Nolte go head to head to find and report the most interesting and amusing fishy stories across sources from far and wide—from respected scientific journals to trashy tabloids.

Thanks to infamous drug kingpin Pablo Escobar, Colombia has an invasive species of unusual proportions: hippopotamuses. Like any invasive species, these large, semi-aquatic mammals have the potential to cause environmental damage and threaten native species. In this particular case, however, the hippos may help protect or even restore the Magdalena River.

Let’s start with the backstory on how the hippos got here, because they are native to Africa, not South America. Escobar built himself a kind of Shangri-La at his Hacienda Napoles, complete with a menagerie of exotic animals from all over the world. After his death in 1993, the Colombian government took over the estate. Although the vast majority of the animals were relocated to zoos, four hippopotamuses were allowed to remain, mostly because capturing and transporting them was difficult, expensive, and dangerous. 

In an NPR interview, Emma Clifford, founder and director of Animal Balance, spoke on efforts to control the hippos. “There were attempts in the past to cull the hippos, but locals were outraged after soldiers shot one. Now it’s illegal to kill them. So scientists are working on a birth control plan for the pachyderms. It’s no small task.”

Over the past few decades, the hippos have thrived, with an estimated population of  80 to 100 individuals, and they are no longer confined to the ponds on Escobar’s former estate. At least half have relocated to the Magdalena, Colombia’s largest and most productive river. 

The Magdalena runs the length of the Western side of the country, it’s the primary river of Colombia and hosts a diversity of native fauna. There are over 200 different species of fish including various cichlids, catfish, and even golden dorado. Unfortunately, those fish aren’t doing so well. Researchers estimate that fish populations have dropped as much as 90% since 1975 for reasons you might expect: pollution, siltation, dams, and illegal overfishing. 

Some researchers are understandably concerned that introducing non-native large animals could further stress a river system that’s already struggling. Hippos transport nutrients into the water. They’re herbivores that wander the land at night, grazing on plants and grasses, and spend the daylight hours sleeping, lounging, and pooping in the water. 

Their poop carries nutrients. Too much nutrients in waterways is known as eutrophication. This alters water chemistry, which can cause algae blooms and cyanobacteria, lower dissolved oxygen levels, and even make fish more vulnerable to predators

Hippos are also known as ecosystem engineers: by moving their massive bodies through muddy river channels and floodplains, they can change how water flows, creating or reshaping channels. How this will affect the Magdalena is yet to be determined. 

Finally, some fear the large invaders might displace or compete with other native mammals like manatees and otters.

Another cadre of researchers are not convinced that having hippos around is necessarily bad for the Magdalena River. Keep in mind, the Magdalena is already pretty screwed up. Some hypothesize that hippos may be re-filling a niche. Up to a dozen large herbivores once roamed South America, like the hippo-looking toxodon, which may have been semi-aquatic, and was wiped out about 11,000 years ago. More contemporary examples include tapirs, pig-like herbivores that also love water—they’re currently endangered. Hippos may now perform functions these animals once did: dispersing seeds, moving nutrients around, and grazing streamside vegetation. 

Hippos are definitely helping out fish in the Magdalena in one particular way: they’re scaring the crap out of poachers. 

Before the hippos started proliferating, illegal dynamite fishing was common. Now, poachers don’t dare try that because hippos are straight up terrifying. You know how moose kill more people in Alaska than bears? Well, hippos kill far more people than the scary predators in Africa. They may not eat people, but they sure do like to chomp, crush, and drown them. 

Hippos fear nothing. My first job out of college was a teaching gig in Botswana, and I naturally went fishing whenever time allowed, which instilled a healthy fear of hippos. I saw one chase a 30-foot double-decker cruise boat, and the boat blinked first. Hippos are more intimidating than any other creature I’ve ever encountered, including bears and sharks. So far, no one has been mauled by a hippo in Colombia, but it’s only a matter of time.

I generally oppose introducing invasive species to try and fix problems humans have created in system balance. So, the following statement may be rightly viewed as hypocritical, but I am provisionally in favor of these hippos colonizing this river, at least for now. The river’s in pretty bad shape already, and biologists think it’s unlikely that the hippo population will get completely out of control because they’re geographically restricted by the river valley. The Andes mountains provide a solid barrier to the east, so there’s no danger of them getting into the Amazon Basin, which would be a legitimate disaster. 

My perspective, and that of certain researchers? Continue to monitor the situation and see how it plays out. If things get worse—the manatees start dying off, the water chemistry gets out of whack, or the fish start disappearing further—then kill the hippos. In the meantime, let the pachyderms keep on terrifying poachers.

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Feature image via Said Alamri.