Some 5,000 to 6,000 broad-snouted caimans live in fetid lagoon systems of western Rio de Janeiro, conservationists say, and there's a chance that visitors 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 already taken refuge in ponds being built inside the Olympic golf course, which abuts a once pristine mangrove-filled lagoon that's now thick with tons of raw sewage pumped from nearby high-end condominiums.
In fact, with two decades of anarchic growth decimating natural habitats, the hardy caimans have become an increasingly common sight in the urban heart of western Rio, drawn in part by the scraps tossed to them by humans.
The district is the main hub for 2016 Games and site of the Olympic village, though most events will take place in indoor facilities. One exception is the golf course, where some caimans have taken up residence in lakes. Wildlife on golf courses isn't uncommon, with alligators spotted on greens in Florida and kangaroos bounding around courses in Australia.
Conservationists say Olympic organizers are beginning to examine what to do about the reptiles on the still-unfinished golf course.
The caimans congregate in a canal in the affluent Recreio dos Bandeirantes suburb that's sandwiched between two busy thoroughfares. Beach-bound mothers with toddlers in strollers, neighbors out to walk the dog and pizza delivery boys pause on a narrow wooden footbridge over the canal to observe the caimans, whose brown color camouflages them in the brackish, sulfuric waters.
With few fish surviving in the polluted waters, caiman increasingly rely on handouts from humans, which can range from raw chicken to crackers, sometimes still in their plastic packages. They also feed on birds and the sewer rats that emerge from the culverts.
"Caimans are like tanks, a very old species with a remarkable capacity for renovation that allows them to survive under extreme conditions where others couldn't," said Ricardo Freitas, an ecology professor who runs the Instituto Jacare, or the Caiman Institute, which aims to protect the reptiles. "But the fact of the matter is that their days are numbered if things don't change drastically."
With a population that's 85 percent male, a serious demographic problem is looming for Rio's caimans, said Freitas, who suspects that the uncontrolled release of raw sewage is behind the gender imbalance. Organic matter raises water warmer and among caimans, high temperatures during a certain stage of incubation result in male offspring.
While a few caimans wander from the canal, sometimes getting hit by cars, Freitas said he is aware of only one other person attacked by a caiman, a fisherman who was superficially bitten after he stepped on one.
Freitas himself has grabbed and tagged 400 of the reptiles over the past decade. He wades into the toxic sludge, slips a metal lasso around their heads and taps expertly on their snapping jaws until he's able to tape them shut. While local caimans average about 1.5 meters (4.9 feet) long and weigh about 10 kilograms (22 pounds), older males can be up to twice as long and much heavier. Still, Freitas has been known to dive into the water to catch some with his bare hands.
"I was only bitten once, on the hand," he said. "It was fine, although it got super infected because of the state of the water."
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