The Connecticut River is the largest and longest river in New England, and also an American Heritage River. It has a total length of 407 miles (655 km), and a drainage basin extending over 11,250 square miles (29,100 km²). The mean freshwater discharge into Long Island Sound is 19,600 cubic feet (560 m³) per second.

It flows roughly south, starting from the Fourth Connecticut Lake in northern New Hampshire. After flowing through the remaining Connecticut Lakes and Lake Francis and leaving the town of Pittsburg, it defines the border between the states of New Hampshire and Vermont. The river then flows through the fertile Pioneer Valley of western Massachusetts and past Springfield, the most populous city on the river. 4 miles (6 km) south of Springfield, the river enters Connecticut, where it spurred the growth of Hartford, the second largest city (and only state capital) along the river. From Hartford, the Connecticut River veers southeastward and ultimately discharges into Long Island Sound at Old Saybrook and Old Lyme, Connecticut.