 Mill River, which drains Weymouth Great Pond (elevation ), and Old Swamp River, both enter Whitmans Pond (elevation ), the latter is the source of Weymouth Back River.After Weymouth Back River becomes a tidal river it receives Fresh River from the right as one heads downstream.The river is part of the Weymouth Back River Area of Critical Environmental Concern (about 950 acres), of which some are tidal waters.