Southwest Branch Saint John River
General data
- Name: Southwest Branch Saint John River
- Water system: Atlantic Ocean
- Water type: River
- Progression: Saint John River (Bay of Fundy) -> Bay of Fundy -> Gulf of Maine -> Atlantic Ocean -> Planet Earth
- Climates: Temperate
- Continents: North America
- Countries: Canada, United States of America
The Southwest Branch Saint John River is a 62.0-mile-long (99.8 km)[1] river in Maine and Quebec. The branch originates in Little Saint John Lake on the international boundary between Saint-Zacharie, Quebec and Seboomook Lake Township 5, Range 20, WELS. The branch forms the Canada–United States border as it flows northeasterly to a confluence with the Little Southwest Branch Saint John River in Seboomook Lake Township 9, Range 18, WELS. The Southwest Branch flows briefly into Quebec and then through Maine to its confluence with the Baker Branch Saint John River in Seboomook Lake Township 9, Range 17, WELS. The Southwest Branch finally joins with the Northwest Branch to form the Saint John River.