I believe only one of the Jersey shark attacks took place inland, and the water there was brackish rather than properly fresh. The body of water in question is named Matawan on the map but was known locally as Shark Creek, and tiger sharks bred there, the fry routinely swarming around the fishing pier. No one was afraid of the sharks of Shark Creek - they were too small and too familiar with humans to be dangerous. The one who did the damage had to be a newcomer.
The author of the book that first gave me this information (library; don't recall the title or author) concluded that the shark attacks that summer were all down to great whites, but no one got a good look at any of the sharks during the attacks. The one hooked in New York with a man's leg in its stomach was a white, but the author saw no reason to assume it was responsible for all the attacks. He used the description of the shark's behavior by the boys in the creek attack (it bit off a kid's leg; thanks to prompt action by his friends his life was saved) as his basis for the great white identification, but admits that other people just as smart as him have studied the same evidence and plumped for bull or tiger sharks.
The book I actually own (Close to Shore by Michael Capuzzo, Broadway Books, 2001) treats the perp as a great white that acted alone, but it's written and marketed in such a way that one must concede the possibility that the dramatic possibilities of the narrative influenced the author's interpretation of the data.
A shark that was feeling sluggish might be more, rather than less, inclined to snap at unsuitable prey like the human leg just to get something inside it and get enough energy to get back to proper salty water. Sharks don't want to eat us, you know - we're too bony, especially the parts that are easiest to grab, the limbs. The trouble is that by the time they've tested us with their teeth and spat us out as unsuitable, they've generally done so much damage that if we don't die we're mutilated for life.
