The Oude Maas (Dutch pronunciation: [ˌʌudə ˈmaːs]; English: Old Meuse) is a distributary of the river Rhine, and a former distributary of the river Maas, in the Dutch province of South Holland.

It begins at the city of Dordrecht where the Beneden Merwede river splits into the Noord and the Oude Maas.

During the later Middle Ages, a flooding event caused the Oude Maas to connect to the Merwede rivers.

However, after the St. Elizabeth's floods the Merwede found a new and shorter path to the sea (the current Hollands Diep).

As a result, the Oude Maas was devoid from much of the inflow of fresh water and changed into a brackish estuary.