I still believe that Disney is the safest environment for a family vacation. We used to swim in Bay Lake all the time, and the only thing that hinted that there could be danger in the water was the swimming area floats held up netting under the water to separate the swimmers from the wildlife. We knew though. All it takes is a simple look at the maps to see that Disney property is the northern most area of the swamps, and we've all seen plenty of National Geographic specials on Alligators to know where they live and how well they can hide/spring at prey. quite impressive really. No research needed.
It's near impossible for Disney to keep indigenous species off the Disney property, especially considering how large it is. Alligators are a great example: they can slip through fences, channels and waterway management systems with ease. Storms cause water areas to overflow and water, one of the most perfect tools of destruction easily rips down barriers put in its way. A small gator is independent and grows quickly. They're hard to detect even by expert trackers, and the most successful critters can stay hidden for ages.