Formation and description
Technically a drowned valley, like the other waterways around New York City, the strait was formed approximately 11,000 years ago at the end of the Wisconsin glaciation. The distinct change in the shape of the strait between the lower and upper portions is evidence of this glacial activity. The upper portion (from Long Island Sound to Hell Gate), running largely perpendicular to the glacial motion, is wide, meandering, and has deep narrow bays on both banks, scoured out by the glacier's movement. The lower portion (from Hell Gate to New York Bay) runs north-south, parallel to the glacial motion. It is much narrower, with straight banks. The bays that exist, as well as those that used to exist before being filled in by human activity, are largely wide and shallow.
A navigation map for Hell Gate
from c.1885, after many of the obstructions had been removed.
The section known as "Hell Gate" – from the Dutch name Hellegat meaning either "bright strait" or "clear opening, given to the entire river in 1614 by explorer Adriaen Block when he passed through it in his ship Tyger – is a narrow, turbulent, and particularly treacherous stretch of the river. Tides from the Long Island Sound, New York Harbor and the Harlem River meet there, making it difficult to navigate, especially because of the number of rocky islets which once dotted it, with names such as "Frying Pan", "Pot, Bread and Cheese", "Hen and Chicken", "Nigger Head", "Heel Top"; "Flood"; and "Gridiron", roughly 12 islets and reefs in all, all of which led to a number of shipwrecks, including the British frigate Hussar which sank in 1780 while carrying gold and silver intended to pay British troops. The stretch has since been cleared of rocks and widened. Washington Irving wrote of Hell Gate that the current sounded "like a bull bellowing for more drink" at half tide, whilte at full tide it slept "as soundly as an alderman after dinner." He said it was like "a peaceable fellow enough when he has no liquor at all, or when he has a skinful, but who, when half-seas over, plays the very devil." The tidal regime is complex, with the two major tides – from the Long Island Sound and from the Atlantic Ocean – separated by about two hours; and this is without consideration of the tidal influence of the Harlem River, all of which creates a "dangerous cataract", as one ship's captain put it.
The river is navigable for its entire length of 16 miles (26 km). In 1939 it was reported that the stretch from The Battery to the former Brooklyn Navy Yard near Wallabout Bay, a run of about 1,000 yards (910 m), was 40 feet (12 m) deep, the long section from there, running to the west of Roosevelt Island, through Hell Gate and to Throg's Neck was at least 35 feet (11 m) deep, and then eastward from there the river was, at mean low tide, 168 feet (51 m) deep.
The broadness of the river's channel south of Roosevelt Island is caused by the dipping of the hardy Fordham gneiss which underlies the island under the less strong Inwood marble which lies under the river bed. Why the river turns to the east as it approaches the three lower Manhattan bridges is currently geologically unknown.
In the stretch of the river between Manhattan Island and the borough of Queens, lies Roosevelt Island, a narrow (maximum width 800 feet (240 m)) 2-mile (3.2 km) long island consisting of 147 acres (0.59 km2). Politically part of Manhattan, it begins at around the level of East 46th Street of that borough and runs up to around East 86th Street. Formerly called Blackwell's Island and Welfare Island, and now named after President Franklin Delano Roosevelt, it was the site of a penitentiary, and a number of hospitals, but now consists primarily of apartment buildings, park land, and the ruins of older buildings. It is connected to Queens by the Roosevelt Island Bridge, to Manhattan by the Roosevelt Island Tramway, and to both by a subway station. The Queensboro Bridge runs across Roosevelt Island, but no longer has a passenger elevator connection to it, as it did in the past. The abrupt termination of the island on its north end is due to an extension of the 125th Street Fault.
Other islands in the river are U Thant Island – formerly Belmont Island – south of Roosevelt Island, which was named after U Thant, the former Secretary-General of the United Nations; and Mill Rock, Wards and Randalls Islands, which have been joined together by landfill, and are used as park land, for a stadium, and to support the Triborough Bridge and the Hell Gate Bridge, Rikers Island, a small island bought by the city in 1884 to be a prison farm and expanded with landfill from under 100 acres (40 ha) to over 400 acres (160 ha), which is currently the site of the city's primary jail, and North and South Brother Islands, all of which lie north of Roosevelt Island.
The Bronx River drains into the East River in the northern section of the strait, and the Flushing River, historically known as "Flushing Creek" empties into it near LaGuardia Airport via Flushing Bay.
North of Randalls Island, it is joined by the Bronx Kill. Along the east of Wards Island, at approximately the strait's midpoint, it narrows into a channel called Hell Gate, which is spanned by both the Robert F. Kennedy Bridge (formerly the Triborough), and the Hell Gate Bridge. On the south side of Wards Island, it is joined by the Harlem River.
Newtown Creek on Long Island drains into the East River, and forms part of the boundary between Queens and Brooklyn. The Gowanus Canal was built from Gowanus Creek, which emptied into the river. Historically, there were other small streams which emptied into the river – including the Harlem Creek, one of the most significant tributaries originating in Manhattan – but these and their associated wetlands have been filled in and built over.