Passaic River, a river in northeastern New Jersey. Its source is in the Piedmont plateau. The river flows south, north, and east, turns south again at Paterson (where the 70-foot [21-m] Great Falls of the Passaic occur), turns east at Newark, and flows into Newark Bay. Its total length is 100 miles (160 km). The Passaic River provided power for the early industrial development of the area (particularly Paterson).