The South River is a 10.6 mi river in eastern New Hampshire and western Maine in the United States. It is a tributary of the Ossipee River, which flows east to the Saco River and ultimately the Atlantic Ocean. The South River begins at the outlet of Province Lake in the town of Effingham, New Hampshire, and proceeds north past the village of Center Effingham. Jogging east, the river enters Parsonsfield, Maine, then turns north again to reach the Ossipee River.