The Merrimack River is the second largest river in New England, draining a total area of 5,014 square miles extending from the White Mountain region of New Hampshire to east-central Massachusetts. The river, which bisects the lower third of New Hampshire, begins at the confluence of the Pemigewasset and Winnipesaukee Rivers in Franklin. It flows for 116 miles before entering the Atlantic Ocean in Newburyport, Massachusetts. 
The Merrimack River played a pivotal role in the early settlement and subsequent development of the region. The river and its banks provided many resources for early inhabitants, including fish, migratory birds, and an important route for communication and transportation. 
Native American sites, cellar holes, cemeteries and the remains of a canal navigation system are included among the prehistoric and historic sites which offer additional historic knowledge of the river and its corridor. Of particular interest are the Naticook Islands, just downstream of the Depot Street public access in Merrimack, which are said to have been the summer home of the great Native American Chief Passaconoway. Another historical highlight of the area are the locks at Cromwells Falls, renowned by The American Canal Society as the best remaining specimen of the Merrimack River Navigation System.