"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 centre of the estuary, whereas the Germans claim it runs through the deepest channel (which is close to the Dutch coast). As the parties are now friendly states with an open border, the argument goes no further than an agreement to disagree.
It became an active issue in late July, 1914, when the Imperial German government began plans to mine the whole of the estuary that they claimed, in preparation for the launching of the Great War. The Dutch envoy in Berlin, Wilem Alexander Frederik Baron Gevers tactfully announced the boundary was uncertain, and that the dispute was "opgeschort", which could mean either 'suspended' or 'resolved', depending on the context. The Dutch government endorsed the ambiguous declaration, thus relieving itself of an obligation to declare war on Germany for violating its neutrality. After the war, the dispute was resumed."
Current status is that the two countries have formally agreed to disagree (https://www.dur.ac.uk/ibru/news/boundary_news/?itemno=22677)