High Quality Content by WIKIPEDIA articles! 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.