The Quinapoxet River is part of the Nashua River watershed in northern Massachusetts in the United States. It is part of the Massachusetts Water Resources Authority water system supplying drinking water to the greater Boston area.

The Nashua River, 37.5 miles (60.4 km) long, is a tributary of the Merrimack River in Massachusetts and New Hampshire in the United States. It is formed in eastern Worcester County, Massachusetts, at the confluence of the North Nashua River and South Nashua River, and flows generally north-northeast past Groton to join the Merrimack at Nashua, New Hampshire. The Nashua River watershed occupies a major portion of north-central Massachusetts and a much smaller portion of southern New Hampshire.