The Federal Dam is a manmade dam

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

 built across 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...

 in the US state of New York

New York

New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...

 from Troy

Troy, New York

Troy is a city in the US State of New York and the seat of Rensselaer County. Troy is located on the western edge of Rensselaer County and on the eastern bank of the Hudson River. Troy has close ties to the nearby cities of Albany and Schenectady, forming a region popularly called the Capital...

 on the east bank to Green Island

Green Island, New York

Green Island is a coterminous town and village in Albany County, New York, USA some 8 miles north of Albany, New York. Green Island is one of only five such town-village amalgams in New York. The population was 2,620 at the 2010 census...

 on the west bank. The major function of the dam is to improve navigability. It is located at mile 153 of the Hudson River, measuring from the beginning of the Hudson as a Federally Navigable Waterway near the Battery in Manhattan

Manhattan

Manhattan is the oldest and the most densely populated of the five boroughs of New York City. Located primarily on the island of Manhattan at the mouth of the Hudson River, the boundaries of the borough are identical to those of New York County, an original county of the state of New York...

. The location of the dam marks the northern end of the Hudson River estuary

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

.
In order to allow ships to move freely, the eastern end of the dam contains a lock

Lock (water transport)

A lock is a device for raising and lowering boats between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a fixed chamber in which the water level can be varied; whereas in a caisson lock, a boat lift, or on a canal inclined plane, it is...

, commonly called the Federal Lock or (on some charts and publications) the "Troy-US Lock." The lock, which was opened in 1916, has a single chamber and is 520 feet (158.5 m) long, 45 feet (13.7 m) wide, 17 feet (5.2 m) deep, and has a lift of approximately 14 feet (4.3 m).