| South Branch Blackwater River | |
| Mouth Location: | Blackwater River |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Length: | about 9miles |
The South Branch Blackwater River is an 8.9adj=midNaNadj=mid[1] river in Aroostook County, Maine. From its source (46.423°N -68.142°W) in Maine Township 9, Range 3, WELS, the stream runs northwest to its confluence with the North Branch to form the Blackwater River in Squa Pan Township (T. 10, R. 4, WELS). Via the Blackwater River, St. Croix Stream, and the Aroostook River, the South Branch is part of the Saint John River watershed.