The Merwede (etymology uncertain, possibly derived from the ancient Dutch Merwe or Merowe, a word meaning "wide water") is the name of several connected stretches of river in The Netherlands, between the cities of Woudrichem, Dordrecht and Papendrecht. The river is part of the Rhine–Meuse–Scheldt delta and is mostly fed by the river Rhine.
At first, a disconnected branch of the Meuse joins the Waal at Woudrichem to form the Boven Merwede (Upper Merwede). A few kilometers downstream it splits into the Beneden Merwede (Lower Merwede) on the right and the Nieuwe Merwede (New Merwede) on the left. All these rivers are tidal. The Nieuwe Merwede joins the Bergse Maas near Lage Zwaluwe to form the Hollands Diep estuary, and separates the Island of Dordrecht from the Biesbosch National Park. The Beneden Merwede splits into the Noord River and Oude Maas near Papendrecht.