Coordinates: 42°50?27?N 70°55?32?W / 42.84083°N 70.92556°W / 42.84083; -70.92556 The Powwow River is a 22.8 mile long (36.7 km)[1]river located in New Hampshire and Massachusetts in the United States. It is a tributary of the Merrimack River, part of the Gulf of Maine watershed.