The Cochecho River or Cocheco 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.