In Article 5 of the Paris Peace Treaty of 30 May 1814 the Contracting Parties agreed to establish a regime of free navigation on the Rhine, at the same time giving a mandate to the forthcoming Congress of Vienna to establish similar navigation regimes for other rivers “which, in their navigable course, separate or traverse different States”. This idea was given substance in the definition of the international regime in the Final Act of the Congress of Vienna of 9 June 1815. Article 108, in particular, speaks of States “separated or traversed by the same navigable river”, while Article 109 provides that “the navigation of the rivers, along their whole course, referred to in the preceding article, from the point where each of them becomes navigable, to its mouth, shall be entirely free … ” So, the application of the rules of free navigation is dependent upon two criteria: the first, of a physical character, is that the water-course possesses by reason of its natural conditions the technical qualities summarized in the word “navigability”. The seond, of a political character, is the condition that the water-course borders on or passes through more than one State. But, in conformity with the basic idea of the Act of Vienna, which regulates the navigation of rivers on the basis of the community of interests of the riparians, for a waterway to be governed by this Act it is necessary that one and the same section of it fulfils both criteria. Consequently, a water-course, the non-navigable upper course of which traverses one State while the whole of its navigable course is in the territory of another State, is not covered by the Act of Vienna.
