According to this article several potent Nile crocodiles have been found snooping around in the lovely Everglades of Florida. http://www.orlandosentinel.com/news/breaking-news/os-crocodiles-everglades-20160519-story.html
Apparently regular American alligators, American crocodiles, snakeheads, invasive Burmese pythons and other critters aren't enough already. As a good rule of thumb, for every croc you do see, there are probably a passel more than you are not seeing. Ecologically these things coming over here will be pretty disastrous. Good luck getting rid of them if they get a foothold here. For reasons I've never been able to fathom American crocs are very timid animals and are almost never aggressive towards humans. I'd be surprised if none of them ever tried taking a snap at someone way back in the day when people walked in leather boots and tri-corner hats, but in general these critters aren't too bad.
Gators can be mighty snippy though and have taken a few humans in the years, but these are nothing like the Nile croc. The article states that around 200 humans are taken each year in Africa by Nile crocs. Ha! At best that's a conservative estimate. Believe it or not, most of the countries throughout the southern half of Africa don't send bureau census takers out into every village and niche in the scrub to find out who gets killed by what for proper records. In reality dozens of people are taken every month throughout the continent. So there are tons of attacks that go unreported. Also they tend to not like to advertise that sort of thing. Bad for tourism you see. Peter Capstick, who spent years in the 70's as a professional hunter in Zambia and Bostwana, mostly the Okavango Delta, became intimately familiar with the habits of crocs and supposed that ten people were taken per day total!
I know for a fact in one region one person was being killed per day, even outside the water. Nile crocs are nothing if not determined buggers. So what will happen if they establish themselves here? Expect hippies to start getting eaten. See, us Americans are spoiled when it comes to game. Our snakes are less venomous and aggressive than in any other country barring Canada and Iceland. American wolves are pacifists unlike European wolves which have killed hundreds of people. Mountain lions don't do jack in comparison to African lions or Asian leopards. Only twelve confirmed kills? You lazy jerks. No native big constrictors, even though even Australia has a few. Even our sharks are underachievers. Sure, there were a few attacks in New Jersey. In the nineteen aughts. We don't get cool things like the Nicaraguan river shark, Ganges shark, or Zambezi river shark. At least we have some bears that occasionally get off their lazy arses and get their man-eater on. Have fun with that Timothy Treadwell! Ha!
But this relatively tame landscape is part of what has led many Americans to believe animals are rarely dangerous. You'll notice that there aren't many members of PETA in the depths of Brazil or Papua New Guinea. We really haven't had to deal all that much with the idea of animals eating us. But if Nile crocs branch out here? Well, that's going to change things. You can bet your boots that just because they are in the land of freedom that they'll change their culinary habits. At best we can expect a lot of cattle and house pets vanishing at a greater rate. I'd love to see PETA or the ALF try to humanize crocodiles with them nabbing a kid's dog right off of the side of a lake. Which will happen.
Personally, I think most Americans need to harden up. Now this is just wishful thinking on my part. I don't think Niles are going to get too well established here. At least not right now. Maybe in a few decades we'll have a few notable man-eaters, but you can count on that news being pretty well repressed. Ah well. Think we can import any other dangerous wildlife here? I heard jaguars are making a slow come back, but they are underachievers too. Think we could import some African leopards?