Two variations on Northern Water Snakes (Nerodia sipedon). The first was warming up ashore on a cool spring morning.
The second was swimming between the sedge tussocks.New Jersey has 22 species of snakes, according to a NJ Fish & Wildlife pamphlet we picked up at Great Swamp NWR. Historically, there was at least one more, the Queen, which is now considered extirpated in the state.
Thanks for identification help from David Steen, whose blog is all about snakes.