A broad-snouted caiman swims in a water channel in the affluent Recreio dos Bandeirantes suburb of Rio de Janeiro, Brazil.

About 6000 caimans live in fetid lagoon systems of the city, conservationists say, and there's a chance that spectators and athletes at the 2016 Olympics could have an encounter with one, though experts hasten to add that the caimans, smaller and less aggressive than alligators or crocodiles, are not considered a threat to humans.

Some of the animals have taken refuge in ponds being built inside the Olympic golf course, which abuts a lagoon that's now thick with raw sewage pumped from condominiums.

- AP