The narrator at the end says that the crocodiles look very hungry. However when you see these "crocodiles" they are actually alligators because of their rounded snout.
The alligators showing at the beginning of are clearly fake. Only until they cut, do you see actual footage of an alligator. The same is true at the end. When Robin is standing above the alligators on the plank, they are clearly fake. Another cut and you see footage of an alligator.