You must live where crocodilians don't exist.
The last time I was in Costa Rica, there was a drainage ditch where dogs frequently disappeared. From time to time a person would be taken. There's one bridge where to water below is rife with them and people feed them chickens off the bridge.
Even closer to home, this happens in Florida all the time. People who weren't used to Florida would let their small dogs roam around free, and if they got near a drainage canal, they became alligator food, much to the owner's surprise. As much as I miss living in Florida (I think Florida is awesome), I would never let my chickens free-range there, LOL.