The Westfield River is a major tributary of the Connecticut River located in the Berkshires and Pioneer Valley regions of western Massachusetts. With four major tributary branches that converge west of the city of Westfield, it flows 78.1 miles (125.7 km) before its confluence with the Connecticut River at Agawam, across from the city of Springfield's Metro Center district. Known for its whitewater rapids and scenery, the Westfield River provides over 50 miles (80 km) of whitewater canoeing and kayaking, in addition to one of the largest roadless wilderness areas remaining in the Commonwealth.

The Connecticut River is the longest river in the New England region of the United States, flowing roughly southward for 406 miles (653 km) through four states. It rises 300 yards south of the U.S. border with Quebec, Canada, and discharges at Long Island Sound. Its watershed encompasses 11,260 square miles (29,200 km2), covering parts of five U.S. states and one Canadian province, via 148 tributaries, 38 of which are major rivers. It produces 70% of Long Island Sound's fresh water, discharging at 18,400 cubic feet (520 m3) per second.