Sailing up the East River leaving the downtown Manhattan bridges and skyline in our wake. We call the East River a river but it's not really a river. It's a salt-water tidal strait that connects New York Bay with the Long Island Sound. Both the bay and sound open to the Atlantic Ocean.
The waters of the Atlantic Ocean, New York Bay, East River, and Long
Island Sound completely surround the large body of land that
Brooklyn, Queens, and "Long Island" sit on. So, technically, Brooklyn & Queens are on the same island as "Long Island." With Staten Island and Manhattan also being islands, this leaves The Bronx as the only part of NYC which is attached to the U.S. mainland.