The authorities in Colombia have sterilized 24 hippos on the former farm of the late drug lord Pablo Escobar.
The animals had multiplied uncontrollably, said the environmental protection organization Cornare on Friday (local time).
Escobar had kept two hippos as well as giraffes, zebras and kangaroos on the farm.
After his death, all animals were sold, except for the hippopotamus.
These reproduced in a herd of 80 animals.
Cornare said that 24 hippos had been given a drug called Gonacon with the aid of arrows.
It is a contraceptive that is effective in both males and females.
Another eleven hippos were sterilized in the conventional way.
Probably the largest hippopotamus herd outside of Africa had caused increasing problems.
“The presence of these animals in an ecosystem that is not their own has consequences like the displacement of the local fauna,” explained Cornare employee David Echeverri.
The animals also attacked fishermen several times.
After Escobar's death in 1993, there had been a dispute over the ownership of his farm, 400 kilometers northwest of the capital, Bogotá.
The private zoo "Hacienda Napoles" was finally opened as an attraction for tourists.