River Oude Maas ("Old Meuse") is a branch in the Rhine-Meuse delta in the Dutch province of South Holland. It begins at the city of Dordrecht where the Beneden Merwede river forks into the Noord River and the Oude Maas.

The Dordtsche Kil forks off soon after Dordrecht. After that the Oude Maas forms the northern boundary of the Hoeksche Waard island, flowing west until the Spui river forks off at the town of Oud-Beijerland. The Oude Maas then heads northwest between the towns/cities of Spijkenisse and Hoogvliet and joins river Nieuwe Maas opposite the city of Vlaardingen, turning into river het Scheur.

The Oude Maas once was the mouth of river Meuse. Nowadays, the Oude Maas is a part of the Rhine river. The river is tidal and has nature and recreation areas.

Connections from the IJsselmonde island on the north:

• with Dordrecht island:
  • road bridge
  • road tunnel
  • railway bridge

• with Hoeksche Waard island:
  • 1st and 2nd Heinenoordtunnel (motor vehicles, cyclists)

• with Voorne-Putten island:
  • Spijkenisser Bridge (motor vehicles, cyclists, pedestrians)
  • metro tunnel