The storm that swept through Rio de Janeiro this week left a wreck in its wake: A landslide swallowed homes, floodwaters rose up in hospitals and power lines collapsed as streets turned into roaring rivers.

Then came the alligators — or, more precisely, their South American cousins, the caimans.

The storm knocked down the walls of a caiman farm in a neighborhood, or favela, that is controlled, like others in Rio de Janeiro, by a heavily armed criminal paramilitary group. This made the local authorities reluctant to enter — and left the creatures, which can grow to be 11 feet long, to swim through the flooded streets, terrifying residents.

The caiman farm stood in the Favela do Rola, in western Rio de Janeiro, one of several sections of the city to be flooded this week. It was unclear how many caimans were bred there, but photographs and videos of the creatures coursing through the floodwaters were shared by several people on social media.

Rejane Guimarães, 38, who has lived in the Favela do Rola for 25 years, said she had spotted two caimans swimming in the murky waters around 10 a.m. Tuesday. She and her neighbors called local officials repeatedly, she said, asking them to remove the creatures.