The [Dordtse Kil]? forks off soon after Dordrecht. After that the Oude Maas forms the northern boundary of the [Hoeksche Waard]? region, 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 the Nieuwe Maas opposite the city of Vlaardingen, flowing into the Nieuwe Waterweg.
The river is tidal and has nature and recreation areas.