Darker blue area shows the location of the Nashua River watershed.

The Nashua River is located in the central highlands of southern New England. The river flows northward into the Merrimack River in Nashua, New Hampshire.

The watershed of a river is a basin in which all precipitation that falls ultimately runs into the river. The Nashua's watershed encompasses 538 square miles and 31 communities in north central Massachusetts and southern New Hampshire, providing drinking water for over one million people.