The South Branch Sunday River is a 2.5 miles (4 km) mountain stream in western Maine

Maine

Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

. It is a tributary of the Sunday River

Sunday River (Androscoggin River)

Sunday River is a river in Oxford County, Maine in the United States. It is a tributary of the Androscoggin River, which flows east and south to join the Kennebec River in Merrymeeting Bay near the Atlantic Ocean....

, which flows to the Androscoggin River

Androscoggin River

The Androscoggin River is a river in the U.S. states of Maine and New Hampshire, in northern New England. It is long and joins the Kennebec River at Merrymeeting Bay in Maine before its water empties into the Gulf of Maine on the Atlantic Ocean. Its drainage basin is in area...

 and ultimately to the Kennebec River

Kennebec River

The Kennebec River is a river that is entirely within the U.S. state of Maine. It rises in Moosehead Lake in west-central Maine. The East and West Outlets join at Indian Pond and the river then flows southward...

 and the Atlantic Ocean

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

.

The South Branch rises on the northern slopes of Bear Mountain, an easterly arm of the Mahoosuc Range, and flows north to the Sunday River in its valley at the foot of the Mahoosucs.