The hydrological distribution of the Maas changed during the later Middle Ages, when a major flood forced it to shift its main course towards the Merwede river.

However, during another series of severe floods the Maas found an additional path towards the sea near Geertruidenberg, resulting in the creation of the Biesbosch wetlands and Hollands Diep estuaries.

The branch eventually silted up, and in 1904 a new parallel channel was dug in the drainage basin, the Bergse Maas.

This channel then took over the functions of the silted-up branch, which has since been known as the Oude Maasje.

At the same time, the branch leading to the Merwede was dammed at Heusden, (and has since been known as the Afgedamde Maas) so that the vast majority of water from the Maas now enters the old Hollands Diep estuary, rather than mixing with the Rhine distributaries.