The Blackwater River is a 37.5 miles (60.4 km) river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 located in central New Hampshire

New Hampshire

New Hampshire is a state in the New England region of the northeastern United States of America. The state was named after the southern English county of Hampshire. It is bordered by Massachusetts to the south, Vermont to the west, Maine and the Atlantic Ocean to the east, and the Canadian...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. It is a tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Contoocook River

Contoocook River

The Contoocook River is a river in New Hampshire. It flows from Pool Pond and Contoocook Lake on the Jaffrey/Rindge border to Penacook , where it empties into the Merrimack River. It is one of only a few rivers in New Hampshire that flow in a predominantly northward direction...

, part of the Merrimack River

Merrimack River

The Merrimack River is a river in the northeastern United States. It rises at the confluence of the Pemigewasset and Winnipesaukee rivers in Franklin, New Hampshire, flows southward into Massachusetts, and then flows northeast until it empties into the Atlantic Ocean at Newburyport...

 watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

.

The Blackwater River is formed at Cilleyville, a village in the western part of the town of Andover

Andover, New Hampshire

Andover is a town in Merrimack County, New Hampshire, United States. The population was 2,371 at the 2010 census. Andover includes the villages of Cilleyville, Potter Place, and East Andover, in addition to the town center...

, by the junction of two branch streams that lack official names on current maps. The western branch begins at the outlet of Pleasant Lake

Pleasant Lake (New London, New Hampshire)

Pleasant Lake is a lake located in Merrimack County in central New Hampshire, United States, in the town of New London. The village of Elkins is located at the east end of the lake, next to its outlet...

 in New London

New London, New Hampshire

New London is a town in Merrimack County, New Hampshire, United States. The population was 4,397 at the 2010 census.The town center, where 1,415 people resided at the 2010 census, is defined as the New London census-designated place , and is located on a hilltop along New Hampshire Route 114 north...

 and flows east through Chase and Tannery ponds in Wilmot Flat

Wilmot, New Hampshire

Wilmot is a town in Merrimack County, New Hampshire, United States. The population was 1,358 at the 2010 census. Wilmot is home to Winslow State Park and a small part of Gile State Forest.-History:...

. The northern stream branch begins at the outlet of Eagle Pond in Wilmot and flows south past West Andover and through Bog Pond, joining the outlet of Pleasant Lake just south of the outlet of Bog Pond. Kimpton Brook (formerly known as Quickwater Brook), flowing easterly through the village of Wilmot Center, is the primary tributary of Eagle Pond.

From its start at Cilleyville, the Blackwater River flows east through the town of Andover, passing the village of Potter Place. Beyond Andover village, the river continues to wind its way east, eventually turning south near the Blackwater Bays and dropping over rapids through the village of West Salisbury to the impoundment area of the Blackwater flood control reservoir in the town of Webster

Webster, New Hampshire

Webster is a town in Merrimack County, New Hampshire, United States. The population was 1,872 at the 2010 census.- History :A part of Boscawen until 1860, the town takes its name from American statesman Daniel Webster.- Geography :...

. Below the reservoir dam, the Blackwater encounters a short, intense whitewater stretch before flattening again for the final miles to the Contoocook in Hopkinton

Hopkinton, New Hampshire

Hopkinton is a town in Merrimack County, New Hampshire, United States. The population was 5,589 at the 2010 census. It consists of three villages: Hopkinton, West Hopkinton, and Contoocook...

.