Since the Parks Department continues to revel in its negligence, we enlisted the help of Jeremy Wade, host of Animal Planet's River Monsters, to help identify the beast. His thoughts:
I've seen nice striped bass come out of the East River, but I can say with authority that this is not a fish, which narrows it down a bit. From my previous incarnation as a biology teacher I can say it's also not a pig: pigs have characteristic cloven feet, which this animal hasn't got. The teeth also look wrong for a pig. From the picture it's hard to get a sense of scale — some kind of rodent would be my guess, and it's common for dead bodies to swell in water, which can give them a grotesque appearance, not to mention crabs etc partially eating soft parts of the face. Not to be ruled out, but unlikely in this case, is the assembly of hybrid animals by taxidermists, from bits of several unrelated creatures. This practice used to be popular in Japan, and I once saw a shrine dedicated to such an animal, not that I'm suggesting that should be the fate of this unfortunate beast.
So if not a dog, or a pig, the creature could also be some hybrid beast made of pig, dog, and rodent parts, most likely sewn together by a sociopathic taxidermist living under the Brooklyn Bridge. At least he didn't say giant catfish.