The East Branch Mattawamkeag River is a tributary of the Mattawamkeag River in Aroostook County, Maine. From its source (46.2307°N, -68.148°W) in Dudley (Maine Township 7, Range 3, WELS), the river runs 36 mi south and southeast to its confluence with the West Branch Mattawamkeag River in Haynesville, about 10 mi west of the Canada–United States border.

Pleasant Lake

Pleasant Lake is the largest lake in the East Branch watershed. The lake extends from the northeast corner of Island Falls into the northwest corner of Maine township 4, range 3. The western edge of the lake overflows 500 yd into the East Branch 5 mi downstream of Oakfield. The lake supports populations of smallmouth bass and rainbow smelt, and is stocked with brook trout and land-locked Atlantic salmon. There is an unimproved boat launch area at the western end of the lake.