The whim of fallen drug lord Pablo Escobar to have hippo in his zoo north of Medellin, in Colombia, is changing the aquatic life of the lakes as their population has exploded from four to more than 80, a new study shows.

When Escobar’s empire came tumbling down, most of the exotic animals in his zoo, including rhino, were relocated, but catching and moving dangerous hippos, which can weigh more than 3,000kg, proved too difficult.

The booming number of hippos is affecting the lake ecosystems and harming the water quality of their South American home, scientists from Colombia and the University of California, San Diego, have found...