WW, are you sure it was a freshwater croc? Saltwater, or estuarine, crocodiles, are found sometimes quite far inland. I've only ever heard of one person being attacked by freshies - it's a far rarer occurrence. People are more likely to be attacked/devoured by salties.
There are signs posted at places where salties are found, warning people - I remember seeing them at Jim-Jim Falls and Twin Falls in Kakadu National Park - but I've never seen a sign warning about freshies. Our guide assured us it was safe to swim at Twin Falls, so we all did - somewhat reluctantly, but the peer pressure was strong (foolish, eh?!). We saw a freshie sacked out on a rock in the river as we set off. It stayed there the whole time we were up at the Falls, so a couple of us had our pictures taken "with" it (very much in the background!) on the way back. Swimming was the only way to get to Twin Falls, and "everybody was doing it"!
I have only ever once heard of someone being attacked, unprovoked, by a freshie, and the theory about that was that the croc had just seen a shadow above it, and thought, "Lunch!" - attacked, then realized it had quite literally attempted to bite off more than it could chew, so left without finishing the attack.
