Final answer:
The Bronx is the only New York City borough not separated from upstate New York by water, unlike Brooklyn, Queens, and Manhattan.
Step-by-step explanation:
The borough of New York City that is not separated from upstate New York by water is The Bronx. Brooklyn, Queens, and Manhattan are each separated by water from upstate New York, making The Bronx the only borough directly attached to the mainland and contiguous with upstate New York. While all five boroughs are part of New York City, The Bronx's geographic connection to upstate New York is unique among them.