The Mianus River is a 20.3-mile-long (32.7 km) river in Westchester County, New York, and Fairfield County, Connecticut, in the United States. It begins in the town of North Castle, New York (east of Armonk) in a series of ponds at about 600 feet (180 m) altitude. Flowing northeast into the town of Bedford, it abruptly turns south and passes through the Mianus River Gorge, a nature preserve, before entering Stamford, Connecticut, where it is dammed into the Mianus Reservoir, officially known as the Samuel J. Bargh Reservoir (256-foot (78 m) altitude) of the Greenwich Water Company. From there, it flows south through Stamford and Greenwich into Long Island Sound, at sea level.