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In the early 1980s, infamous drug lord Pablo Escobar created a family zoo full of exotic animals in Colombia, including rhinos, giraffes, zebras and hippos. When Escobar's empire crashed in the '90s, the animals were relocated to zoos -- except for the four hippos, now considered an invasive species whose waste is wreaking havoc on the Colombian aquatic ecosystem, according to a new study published in the journal Ecology.

Escobar's four hippos have since multiplied to 80 hippos. Researchers from the University of California, San Diego and the Universidad Pedagógica y Tecnológica de Colombia spent two years studying the water quality and microbiomes of lakes with hippo populations, and comparing them to those without. Hippos are nocturnal animals that feed on land during the night and spend their days cooling off in the water, and the large amounts of waste they're excreting into the lakes is changing the water's chemistry and oxygen levels, the researchers found.

It turns out the hippo poop is fertilizing harmful algae and bacteria. This can lead to problematic algae blooms similar to red tides, which cause illness in humans and animals, according to the study.

Hippos are difficult to catch and dangerous to confront, the researchers noted in a press release. The Colombian hippo population will likely continue to grow dramatically in the coming years, which could further change the aquatic ecosystem as they interact more with local animals, like manatees and giant river turtles found in nearby rivers.

"If you plot out their population growth, we show that it tends to go exponentially skyward," Jonathan Shurin, a biological sciences professor at UC San Diego and lead author of the study, said in the release. "In the next couple of decades there could be thousands of them. This study suggests that there is some urgency to deciding what to do about them. The question is: What should that be?"