I remember from when I lived in Orlando, a news article about a pond with ducks in it. The people in the office buildings around it would go and feed the ducks during lunch. They were disappointed when the ducks started moving on. Only later, when officials pulled a gator out of the pond did they realize the ducks hadn't moved on.
My cousins still live in Orlando. When their son was little, they taught him at a young age to not go near the edge of ponds without the parents there. Just too easy to get grabbed by a gator. Heck, as an adult, I was leery around the edge of ponds if I couldn't see into the water.
It is tragic and I really feel for the parents. But even at Disney, you only swim where they say you can. It's just to hard for them to patrol and guarantee a gator won't move in. They try and do a great job, but there is no way to guarantee it 100%. Hence, the no swimming signs they post.