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The Harlem River is a navigable tidal strait in New York City USA that flows 8 miles (13 km) between the Hudson River and the East River separating the boroughs of Manhattan and the Bronx. Part of the current course of the Harlem River is the Harlem River Ship Canal which runs somewhat south of the former course of the river isolating a small portion of Manhattan (Marble Hill) on the Bronx side of the river. Contents 1 Navigation and transportation 2 Geology and natural history 3 History 3.1 Early colonial developments 3.2 19th century 3.3 20th century 4 Recreational uses 5 Crossings 6 See also 7 References Navigation and transportation

The Harlem River is spanned by seven swing bridges three lift bridges and four arch bridges1 and is navigable to any boat with less than 55 feet (16.8 m) of air draft. However any boat requiring more than 5 feet (1.5 m) of clearance will require the Spuyten Duyvil Bridge to swing open. All other movable bridges on the Harlem River provide at least 24 feet (7.3 m) of clearance while closed so boats and ships requiring between 5 and 24 feet (1.5 and 7.3 m) of clearance need only have one bridge swing open. These bridges replaced fixed bridges or lower bridges in the late 19th century to improve navigation. In recent yearswhen test openings of the movable bridges on the Harlem River have outnumbered openings for navigation. There are no fees for navigation of the river. High Bridge was erected between 1837 and 1848 to carry the Croton Aqueduct across the river. It is the oldest bridge in New York City. Three of the bridges that cross the Harlem River are visible in this photo of the river: the High Bridge (a now-closed pedestrian bridge); the Alexander Hamilton Bridge (part of Interstate 95); and the Washington Bridge. In this photo looking north the Washington Heights neighborhood of Manhattan is on the left and the Bronx is on the right

The New York City Department of Transportation advises that while they make every effort to ensure that all bridges are operating many of them are under repair at any time and outside contractors are responsible for opening of bridges under repair. As well sometimes on hot summer days many of the bridge decks seize due to thermal expansion and cannot open or close. Since the city will not allow more than one bridge open at a time a bridge seizing in the open position can potentially leave a mariner stranded in a small section of the river.

Harlem River Drive and Harlem River Greenway run along the right bank of the river and Hudson Line (Metro-North) railroad and Major Deegan Expressway the left. The "C" Rock with the Henry Hudson Bridge behind it and the Spuyten Duyvil Bridge in the distance in the open position. Geology and natural history

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 18000 years ago the Laurentide ice sheet receded northward across the continent leaving behind a large escarpment creating the modern day Hudson River.2 About 6000 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 name river is technically incorrect as the Harlem River has neither a mouth nor a source. It simply connects two larger bodies of water stretching from the Hudson River to the intersection of the East River at Randalls Island at approximately East 125th Street on the present street grid. The Harlem River is therefore affected by the actions of the ocean and neighboring rivers. The ebb and flow of the tides causes the Harlem Rivers 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 navigate in the northern portion of the waterway allowing only smaller ships and experienced sailors.

Stretching approximately seven miles the river originally meandered through its length but the course of the river today is much straighter than it was in its natural state. Changes in the rivers route and shoreline character have reflected the designs of engineers planners politicians and industrialists intent on subverting the limitations of the natural topography to facilitate the flow of commerce and real estate investment. Bulkheads barriers fills and cuts all affected the river changing and manipulating it into its current state. A systematic examination of the changes to the rivers function and access provides an understanding of its revamped role in the urban process. History Early colonial developments

The landmass of Marble Hill once provided a fine location for Native American encampments where fertile soil shelter by hills to the west and the abundance of fishing and oystering options nearby were found.3 By the end of the 17th century most land along the Harlaem River had come under the ownership of the Dutch families whose names are now commonly seen on street signs area maps and parks including Jonas Dyckman Jacob Nagle etc. The British Colonial authorities however eventually wrested control of the island from the Dutch and regulation of waterfront construction became the responsibility of the city; this preceded any formal attempts to standardize shoreline expansion by nearly a century.4

It was in this era that the first crossing on the Harlem was built at the Old Albany Road (north of Marble Hill) in 1693. This came to be called Kings Bridge where a toll was assessed for access to the island and lands south. While this crossing was intended to replace the ferry service provided in the same area from approximately 1669 onward the local population eventually bridled over the toll and popular sentiment culminated in the construction of the Farmers Free Bridge further south along the Spuyten Duyvil Creek in 1758. The shallow waters of the creek along this stretch were thus spanned beginning a long history of bridge construction and physical alterations to the river. Today thirteen bridges cross the Harlem River connecting the boroughs of the Bronx and Manhattan. According to Harpers Weekly in 1882 One of the most striking proofs of the rapid growth of New York is furnished by the bridges of the Harlem.5 There are two general categories of bridge type on the Harlem: fixed arch and movable. Four of the bridges are fixed arch spans (Henry Hudson Alexander Hamilton Washington and High Bridges) and are built at some of the highest points along the river connecting the uplands while remaining high above the water. The other nine are movable bridges (Spuyten Duyvil Broadway University Heights Macombs Dam 145th Street Madison Park Third and Willis Avenue Bridges) and are located at lower grades. At the heart of their construction was the issue of keeping the Harlem River navigable for water traffic and yet sufficiently serving the needs of land bound traffic crossing the river.6 19th century The issue of navigability became a topic of controversy early in the rivers history. In 1813 the Macomb family built a dam to power a mill; however it created a millpond and impeded the rivers flow and open navigation.7 While this condition was tolerated for several years a vessel manned by principal landholders and politicians including Governour and Lewis Morris formally challenged the obstruction in 1838. Legal battles over the legitimacy of the right to obstruct the waterway ensued. Ultimately the testimony of numerous local residents who used the river in transporting lumber fuel raw materials and produce to and from their estates up and down the Harlem helped persuade the courts to rule favorably for unimpeded access to the rivers navigable waters.8 Consequently bridge designs thereafter needed to factor in the rights of waterborne traffic to pass freely an issue that instigated dissent in the future with regards to the efficiency of movable river crossings and the needs of the railroads. The issue of navigability gained urgency with the opening of the Erie Canal in 1825 spurring intense commercialization of the West Side waterfront on the Hudson River as well as interest in creating a faster route to the East River and the Long Island Sound beyond. For the first half of the 19th century the Harlem River basin had remained relatively unaffected by the commercial growth commonplace along the islands south-most waterfront. However public health issues concerning access to water for the burgeoning population and firefighting needs spurred a public works project that would greatly impact the region. A plan for the Croton Aqueduct was finalized in the late 1830s.9 This was a monumental public works project on a scale previously unseen in the United States. The aqueducts crossing at the Harlem River became the most prominent aspect of its course prior to the fountains it supplied downtown. The High Bridge as this crossing came to be known was completed in 1848 to great public enthusiasm and worldwide acclaim. To accommodate the sloops and ferries sailing the river at the time the bridge was required to meet certain minimum heights and widths for its supporting arches. The construction of the Croton Aqueduct presaged the rapid subjugation of the natural landscape to accommodate the needs of economic and population growth in the New York metropolitan area. The Park Avenue Bridge for the New York New Haven and Hartford Railroad was built concurrently opening in 1841 and bringing rails to the Bronx east of the Hudson. The introduction of several rail lines near the Harlem in the following decades spurred growth of industrial and residential districts along the riverfront. The installation of the Harlem Line along the rivers edge completed in 1851 forever changed access to the shore on the Bronx side of the Harlem. The construction of rails on trestles set in rip-rap foundations on the riverbed pushed the trains off the lands edge in favor of an unobstructed course north. These trestles and rip-rap then provided the support for new fill between the rails and the shore. The negative impacts on the shoreline were manifest in the difficulty building new docks or piers which would require at-grade crossings as well as in restricted access to the riverfront which had previously been a resource that benefited residents for generations. During this period anticipated growth in shipping commerce persuaded the city of New York to create the Department of Docks in 1870 as well as adopt a waterfront plan known as the McLellan Plan which envisioned a partially submerged masonry wall around the whole of the island. These new works were not implemented as rapidly along the Harlem River as they were along the shores of the East and Hudson Rivers where the channels were deeper and wider accommodating longer piers. Development of the land around the Harlem River has long been linked to not only the areas topography but also its geology. Composed of three distinct layers of bedrock Manhattan Schist Fordham Gneiss and Inwood Marble6 these rock types were found in outcroppings in the locality and were likely used by the earliest residents for building material as the marble was readily available and easy to tool. In the early 19th century the stone had been quarried in Inwood and Marble Hill to produce both a building material as well as lime mortar. In 1819 the Spuyten Duyvil Creek was widened to provide additional power for the local marble industry. The excavation for the Harlem River Shipping Canal in 1895 directly through an old quarry site also served to provide a large quantity of marble rubble which was used as a building material throughout the area. 20th century The increase of both recreational and commercial traffic along the river at the turn of the 20th century required further manipulation of the shore. The river was dredged formally surveyed and demarcated by the beginning of the 20th century. The northern tip of the waterway called Spuyten Duyvil went through massive changes leading up to the opening of the Harlem River Shipping Canal. This project deepened the river in this area eighteen feet and widened it four hundred feet. As a result of this engineering project a portion of Manhattan was severed from the landmass geographically becoming a part of the Bronx. Today this area is known as Marble Hill and the community there continues to struggle with political boundaries that are split between the boroughs. While the canal helped shape the communities around it in a number of ways its plan came too late to influence the development of port facilities further south which were already committed to a course of growth centered on the railroads. The industrial districts that formed around Mott Haven and Harlem responded most to the presence of the railroad which developed both as a complement and competitor to waterborne trade. Movement of materials goods and people along the axes of Manhattan and the Bronx indicated a flexibility of transport with which shipping could not compete. Despite the movement away from using the waterway for shipping its role as a transportation corridor continued to evolve during the end of the 19th-century. This period saw the height of bridge building as the City of New York stretched into its outermost boundaries and sought ways to make use of available land. The peak in bridge construction lasted from 1880 to 1910 and focused on the swing bridge as the most economical way to reconcile the land-wasteful approaches of tall bridges with the desire to keep the river navigable for taller vessels. Some of these bridges replaced predecessors unable to sustain increased traffic; others were erected at new sites to provide more access points. Yet another was recycled and moved to a new location further down the river. Almost all of these bridges from that era of expansion are in existence today. Most of these bridges were for local traffic and pedestrians and a few accommodated trolley lines. Two were constructed for elevated trains lines prior to the advent of the subway. The more recently built Harlem bridges respond to land bound traffic only as the use of the river as waterway diminished by the late 1920s. The fixed arch Henry Hudson (1936) and Alexander Hamilton (1964) Bridges were added in the later era of automobile highways. Both were intended to relieve traffic congestion in the area but the amount of vehicles quickly increased to fill the temporary lag. Two swing bridges were torn down in the 1950s when their use as elevated train lines was no longer warranted. Two of the more recently constructed bridges (at Broadway and Park Avenue) are vertical lift replacements of swing spans where the previous bridges had become obsolete for the subway and railroad that used them. The evolution of the bridges across the Harlem River reflects its use as an urban transit corridor while a few also conjure its fleeting pastoral reputation. Far more tame than the East or Hudson Rivers the Harlem was not as daunting an obstruction as other rivers. It did not require bridges like the Brooklyn or George Washington that were marvels of long-span engineering. The river required those engineering feats of industrial practicality that would allow for large amounts of vehicles people and goods to efficiently cross over the river and on it. Truly urban in their response to the land they occupy the Harlem River bridges each reflect the metropolis ambitions and needs of their time. On a continual basis those who have settled near its waters have physically molded the Harlem River and taken advantage of its natural topography. While it often seems the infrastructure that once complemented the rivers function now serves to bypass it these ongoing alterations to the resource reflect the history of the object the people who exploited its assets and the manner in which it shaped its bordering communities as well as New York City. The transformation of the waterway through the years suggests its ability to again be adapted for viable uses both commercial and recreational by those that live and work near it. Through enhanced access and usage the Harlem Rivers rich history and significance can be appreciated and honored. Recreational uses The Harlem River was the traditional rowing course for New York analogous to the Charles River in Boston and the Schuylkill River in Philadelphia. On the Harlem's banks is the boathouse for the Columbia University crew and the river is the home course for the university's crew. The "C Rock" refers to a large Columbia varsity "C" painted on a rock face along the tracks used by Metro-North Railroad. Despite commercial developments the Harlem River has been used by many as a major source of recreation. In the year 1902 over 1000 rowers made use of the Harlem River. A number of boat clubs were located along its shores and remained until 1978 when the last boathouse at Sherman Creek burned down. While much can be said about the commercial use of the waterway the recreational facilities that line its shore also contributed to defining its character. The steep cliffs that line much of the area were obvious locations for parkland. The High Bridge shore was developed as a park and speedway on which the well-trained steeds of Manhattans elite could race without pedestrian interference. This is an example of the manner in which the shoreline was sculpted as the rugged edge was united with existing islands to create a landscape in a resort atmosphere from which one could comfortably observe the horse races on land and the sculling in the water. Magnificent arches stairwells and footpaths were constructed to facilitate the leisurely usage of the waterfront. Also on the river are the Peter Jay Sharp Boathouse and Harlem River Community Rowing two community rowing facilities. The river is used by crews from New York University Fordham University and Manhattan College though the only university with permanent facilities on the river is Columbia. In the past Columbia rowers have assisted the New York City Police Department in murder investigations by sighting bodies in the water.citation needed Such occurrences have appeared in the television series Law & Order. Misty morning over the Harlem River Aerial view of the northern part of Harlem River with the larger Hudson River close by in the background Crossings Main article: List of crossings of the Harlem River See also Geography of New York Harbor List of New York rivers References Wikimedia Commons has media related to: Harlem River Sharon Reier: The Bridges of New York: Dover Press; 1977. Tobin Mary. 2004. Hudson River Estuary enters Middle Age. The Earth Institute at Columbia University. Retrieved April 12 2004 from Columbia University. http://www.earthinstitute.columbia.edu/news/2004/story02-05-04.html Bolton Reginald Pelham. Washington Heights: Its Eventful Past New York Dyckman Institute 1924. p.206. Bone Kevin. The New York Waterfront: Evolution and Building Culture of the Port and Harbor New York The Monacelli Press Inc. 1997 p.265. Across the Harlem Harpers Weekly 26.1352 (November 15 1882) 731. a b http://www.gsapp.org/Archive/HP/2003-2004/history.html Hermalyn Gary. The Harlem River Ship Canal The Bronx Historical Society Journal Volume XX #1 Spring 1983. Morris Lewis G. Harlaem River: Its Use Previous to and Since the Revolutionary Wat and Suggestions Relative to Present Contemplated Improvement. New York J.D. Torrey 1857. p. 38. Gandy Matthew. Concrete and Clay. Boston Massachusetts Institute of Technology 2002. p.33. Coordinates: 405005.00N 735602.85W / 40.83472N 73.934125W / 40.83472; -73.934125