Harlem River
Coordinates: 40°50′05.00″N 73°56′02.85″W / 40.8347222°N 73.9341250°W
The Harlem River is an 8-mile (13 km) tidal strait flowing between the Hudson River and the East River and separating the island of Manhattan from the Bronx on the New York mainland.
The northern stretch, also called the Spuyten Duyvil ("spewing devil") Creek, has been significantly altered for navigation purposes. Originally it curved round the north of Marble Hill, but in 1895 the Harlem River Ship Canal was dug between Manhattan and Marble Hill, and in 1914 the original course was filled in.
The Harlem River forms a part of the Hudson estuary system, serving as a narrow strait that divides the island of Manhattan from the Bronx. Approximately 18,000 years ago the Laurentide ice sheet receded northward across the continent leaving behind a large escarpment creating the modern day Hudson River. About 6,000 years ago the Hudson River emptied into the ancient Atlantic Ocean, depositing sediments over the bedrock; this resulted in the formation of the Hudson River estuary, which is the water and land at the mouth the river that contains a mixture of salt and freshwater, including the Harlem River.
The "river" is actually an estuary, as the Harlem River has neither a mouth nor a source, but instead connects two larger bodies of water, the Hudson River, via the Spuyten Duyvil Creek, to the East River – which is itself not a river, but a salt water tidal strait – at Randall’s Island, near 125th Street. The Harlem River is therefore affected by the actions of the ocean and neighboring waterways. The ebb and flow of the tides causes the Harlem River’s currents to fluctuate dramatically throughout the day. The effects of the tides have influenced the spread of silts, pollutants, and other particles in the water. The tides were also important in defining the usage of the Harlem River as they caused the currents to be particularly difficult to navigate in the northern portion of the waterway, allowing only smaller ships and experienced sailors. Stretching approximately 7 miles (11 km), the Harlem River originally meandered through its length, but its course today is much straighter than it was in its natural state due to changes in its route and shoreline character.
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