Cohas Brook is a 16.5 miles (26.6 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 southern 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 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...

, part of the Gulf of Maine

Gulf of Maine

The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...

 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...

.

Cohas Brook rises in Auburn, New Hampshire

Auburn, New Hampshire

Auburn is a town in Rockingham County, New Hampshire, United States. The population was 4,953 at the 2010 census. The town was called by WMUR News 9 as number one of "New Hampshire's Most Beautiful Towns" in July 2010. It was also named 18 in The New York Times' "Top 200 Towns To Raise a Family."-...

, north of Calef Pond. The brook follows a winding course westward to the Merrimack River in Manchester

Manchester, New Hampshire

Manchester is the largest city in the U.S. state of New Hampshire, the tenth largest city in New England, and the largest city in northern New England, an area comprising the states of Maine, New Hampshire, and Vermont. It is in Hillsborough County along the banks of the Merrimack River, which...

. In Manchester it picks up the outlet of Massabesic Lake

Massabesic Lake

Massabesic Lake is a lake in southern New Hampshire, United States, covering about within the city of Manchester and the town of Auburn. Because it provides drinking water for Manchester, swimming and water skiing are not allowed there. Popular sports on the lake are sailing, fishing, kayaking...

, the water supply for the city. This lower portion was formerly known as Coos River.

Much of the brook's course is quite close to intense suburban development, including Interstate routes 93

Interstate 93

Interstate 93 is an Interstate Highway in the New England section of the United States. Its southern terminus is in Canton, Massachusetts, in the Boston metropolitan area, at Interstate 95; its northern terminus is near St. Johnsbury, Vermont, at Interstate 91...

 and 293

Interstate 293

Interstate 293 is an long loop surrounding Manchester, New Hampshire, USA roughly shaped like two sides of a triangle. Completing the loop in the northeast is Interstate 93. The southern portion of the loop shares the road with NH 101 and passes near Manchester-Boston Regional Airport and the...

, the South Willow Street commercial corridor, and the Manchester Airport

Manchester-Boston Regional Airport

Manchester-Boston Regional Airport , commonly referred to simply as "Manchester Airport," is a public airport located three miles south of the central business district of Manchester, New Hampshire on the county line of Hillsborough and Rockingham counties...

.