The Sawkill or Saw-kill was the largest hydrological network on Manhattan island in New York City before the Dutch colony of New Netherland was founded in 1624. This 44,980-foot-long (13,710 m) stream began "within four blocks of the Hudson River":A rill flowing east from the rocky ridge overlooking Bloomingdale Village, which rose near Ninth Avenue and 85th Street, flowed in a southerly direction through Manhattan Square, where it spread into a little pond, and then turned east, crossing Central Park to Fifth Avenue, receiving three tributaries within its limits, two from the north and one from the south. At 75th Street near Third Avenue it was joined by another stream. Near this junction the old Boston Post Road crossed it, and then from this point, the stream ran due east to its outlet near the foot of 75th Street

The East River is a saltwater tidal estuary or strait in New York City. The waterway, which is actually not a river despite its name, connects Upper New York Bay on its south end to Long Island Sound on its north end. It separates Long Island, with the boroughs of Brooklyn and Queens, from Manhattan Island, and from the Bronx on the North American mainland.