The source of the river is located in the southern Teutoburg Forest in North Rhine-Westphalia. In Lower Saxony the brook becomes a comparatively large river. Here the swampy region of Emsland is named after the river. In Meppen the Ems is joined by its largest tributary, the Hase river. It then flows northwards, close to the Dutch border, into Ostfriesland (Eastern Frisia). Near Emden it flows into the Dutch Dollard bay (a National Park) and then continues as a tidal river towards the Dutch city of Delfzijl.
Between Emden and Delfzijl, the Ems forms the border between the Netherlands and Germany and is subject to mild dispute: the Dutch believe that the border runs through the geographical center of the estuary, whereas the Germans claim it runs through the deepest channel (which is close to the Dutch coast). As both parties are friendly states, the argument goes no further than an agreement to disagree.
Past Delfzijl, the Ems discharges into the Wadden Sea, part of the North Sea. The two straits that separate the German island of Borkum from its neighbours Rottumeroog (Netherlands) and Memmert (Germany) continue the name "Ems", as they are called Westere(e)ms and Osterems (West and East Ems).