longest stream in New England, rising in the Connecticut lakes in northern New Hampshire, U.S. After flowing about 9 miles (14 km) through New Hampshire, it moves roughly southwestward and forms the border between New Hampshire and Vermont for about 238 miles (383 km). It then crosses Massachusetts and Connecticut to empty into Long Island Sound after a total course of 407 miles (655 km).

The river drains an area of 11,085 square miles (28,710 square km). Its 23 principal tributaries, which include the Passumpsic, White, Deerfield, and Farmington rivers (on the right) and the Ammonoosuc and Chicopee rivers (on the left), are mostly short, swift streams in narrow valleys dotted with small power dams, storage ponds, and factories. The Connecticut is one of the most completely developed rivers in the United States in terms of hydroelectric power. Following disastrous floods in 1936, a federal project involving 20 dams and reservoirs was begun. A dam at Wilder, Vt., has a reservoir 46 miles (74 km) long. The lower 60 miles (97 km) of the river are tidal. The name Connecticut supposedly comes from the Mohican (Mahican) Indian word meaning “the long river.”