The Afgedamde Maas (Dammed-up Meuse) is a former distributary of the Maas River (French: Meuse) in the Dutchprovinces of North Brabant and Gelderland. The Maas splits near Heusden with one channel flowing north until its confluence with the river Waal (the main distributary of the river Rhine) to form the Merwede, while the other channel (the Bergse Maas) continues west as the main distributary of the Maas.
The current Afgedamde Maas was created in the late Middle Ages, when a major flood made a connection between the Maas and the Merwede at the town of Woudrichem. From that moment on, the current Afgedamde Maas was the main branch of the river Maas. The former main branch eventually silted up and is today called the Oude Maasje. In the late 19th century and early 20th century the connection between the Maas and Rhine was closed off and the Maas was given a new, artificial mouth - the Bergse Maas. The resulting separation of the rivers Rhine and Maas reduced the risk of flooding and is considered to be the greatest achievement in Dutch hydraulic engineering before the completion of the Zuiderzee Works and Delta Works. The former main branch was, after the dam at its southern inlet was completed in 1904, renamed Afgedamde Maas and no longer receives water from the Maas.