Saw Mill River

The Saw Mill River is a 23.5-mile (37.8 km)^: 9 tributary of the Hudson River in Westchester County, New York, United States. It flows from an unnamed pond north of Chappaqua to Getty Square in Yonkers, where it empties into the Hudson as that river's southernmost tributary. It is the only major stream in southern Westchester County to drain into the Hudson instead of Long Island Sound. It drains an area of 26.5 square miles (69 km²),^: 9 most of it heavily developed suburbia. For 16 miles (26 km), it flows parallel to the Saw Mill River Parkway, a commuter artery, an association that has been said to give the river an "identity crisis."

The watershed was settled by the Dutch in the 17th century. The land was long owned by Frederick Philipse I and his descendants as Philipsburg Manor, site of Philipse Manor Hall, until the family lost it at the end of the American Revolution. The land along the river was later divided into multiple towns. Industry in Yonkers developed along the Saw Mill, so polluting the river by the end of the 19th century that a local poet called it a "snake-like yellow scrawl of scum". In the 1920s, the last half-mile (800 m) of the stream was routed into tunnels and culverts under downtown Yonkers, a process partially reversed in the early 21st century when it became the first major New York waterway to be daylighted.

Today, the U.S. Environmental Protection Agency (EPA) rates the river's last 2.9 miles (4.7 km) as an impaired water body. Plastics are commonly found along the riverbank, and metals from industrial factories are found in the water in high concentrations. Nonetheless, the river is home to species such as the American eel (Anguilla rostrata), which swim upstream to mature and swim back into the Hudson and the ocean in order to breed.