The Cochecho River is a tributary of the Piscataqua River, 38.3 miles (61.6 km) long, in the U.S. state of New Hampshire. It rises in northern Strafford County and runs southeastward, through the town of Farmington and the cities of Rochester and Dover, where it provides hydroelectric power. Below the center of Dover, the river is tidal and joins the Salmon Falls River at the Maine border to form the Piscataqua. Significant tributaries include the Ela River, the Mad River, and the Isinglass River.

The Piscataqua River is a 12-mile-long (19 km) tidal river forming the boundary of the U.S. states of New Hampshire and Maine from its origin at the confluence of the Salmon Falls River and Cochecho River to the Atlantic Ocean. The drainage basin of the river is approximately 1,495 square miles (3,870 km2), including the subwatersheds of the Great Works River and the five rivers flowing into Great Bay: the Bellamy, Oyster, Lamprey, Squamscott, and Winnicut.