The Farmington River is a river, 46.7 miles (75.2 km) in length along its main stem, which is located in northwest Connecticut with major tributaries extending into southwest Massachusetts. Via its longest branch (the West Branch), the Farmington's length increases to 80.4 miles (129.4 km), making it the Connecticut River's longest tributary by a mere 2.3 miles (3.7 km) over the major river directly to its north, the Westfield River. The Farmington River's watershed covers 609 square miles (1,580 km2). The river historically played an important role in small-scale manufacturing in towns along its course, but it is now mainly used for recreation and drinking water. The Farmington River Watershed Association is a non-profit organization for conservation and preservation of this river.