The Narrows is the tidal strait

Strait

A strait or straits is a narrow, typically navigable channel of water that connects two larger, navigable bodies of water. It most commonly refers to a channel of water that lies between two land masses, but it may also refer to a navigable channel through a body of water that is otherwise not...

 separating the boroughs of Staten Island and Brooklyn in New York City. It connects the Upper New York Bay

Upper New York Bay

Upper New York Bay, or Upper Bay, is the traditional heart of the Port of New York and New Jersey, and often called New York Harbor. It is enclosed by the New York City boroughs of Manhattan, Brooklyn, and Staten Island and the Hudson County, New Jersey municipalities of Jersey City and Bayonne.It...

 and Lower New York Bay

Lower New York Bay

Lower New York Bay is that section of New York Bay south of the Narrows, the relatively narrow strait between the shores of Staten Island and Brooklyn. The southern end of the bay opens directly to the Atlantic Ocean between two spits of land, Sandy Hook, New Jersey, and Rockaway, Queens, on Long...

 and forms the principal channel by which the Hudson River

Hudson River

The Hudson is a river that flows from north to south through eastern New York. The highest official source is at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains. The river itself officially begins in Henderson Lake in Newcomb, New York...

 empties into the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

. It has long been considered to be the maritime "gateway" to New York City

New York City

New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 and historically has been the most important entrance into the harbor

Harbor

A harbor or harbour , or haven, is a place where ships, boats, and barges can seek shelter from stormy weather, or else are stored for future use. Harbors can be natural or artificial...

s of the Port of New York and New Jersey

Port of New York and New Jersey

The Port of New York and New Jersey comprises the waterways in the estuary of the New York-Newark metropolitan area with a port district encompassing an approximate area within a radius of the Statue of Liberty National Monument...

.

The Narrows were most likely formed after deposition of the Harbor Hill Moraine about 18,000 years ago prior to the end of the last ice age

Ice age

An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...

.