Mattapoisett is a town in Plymouth County, Massachusetts. The waters off Mattapoisett offer some very good fishing with a variety of species, most notably striped bass, which typically arrive in early May. School bass and some larger fish can be taken inside the Mattapoisett River in May as they follow silversides and migrating herring upstream. Soft-plastics, poppers and jigs all work inside the river at this time. Early morning generally brings the best fishing.