|The concept of an ‘international watercourse’, as derived from Article 2(a) and (b), means the Convention applies to ‘watercourse systems’ that cross international boundaries, including major and minor watercourses, their tributaries,101 and connected lakes and groundwater, even when these individual components are entirely located within a single state. According to the International Law Commission’s commentary to the 1994 ILC Draft Articles, components of freshwater systems that may fall under this concept, when connected to one another, include rivers, lakes, aquifers, glaciers, reservoirs, canals, wetlands and floodplains.102 The test to establish whether a watercourse is ‘international’ depends on physical factors, the existence of which can be established by simple factual and geographical observation in the vast majority of cases, and the word ‘situated’ is not intended to imply that the water is static.103Related to this test is the question of what waters of an international watercourse are situated in the ‘territory’ of a state and how the location of the boundary is to be determined, especially when an international river changes its course. The Convention does not answer these questions; the answers are found elsewhere in international law. The determination of boundaries depends on whether a watercourse is successive or contiguous (meaning whether it traverses or forms boundaries between states respectively). If it is successive and there is no existing agreement to the contrary, then the border is said ‘to cross the river along the shortest line connecting the points at which the borders of the opposite states intersect the banks of the river’.104 If the watercourse is contiguous the most common treaty approach is to locate the boundary along the thalweg105 if the river is navigable, and along the median line if not.If the international watercourse changes its course and this change occurs over a long period of time (by accretion and erosion) then the general rule is the territorial boundary of a state changes with the river.106 If this change occurs suddenly (by avulsion), then the general rule is the boundary remains in the original location.107 It is also important to note that even if it is acknowledged that a state enjoys exclusive competence over utilisation of the waters of an international watercourse in its territory, given that water is constantly in motion, it is very difficult to determine which waters are located within the territory of a state and thus applying concepts of territorial sovereignty to watercourses is very problematic – as discussed in Part II.108
During the drafting of the Convention, the ILC’s efforts to deal with the geographic scope of an international watercourse generated a rich record of discussion within the ILC and the sixth Committee.109 The ILC gathered state opinion on whether the concept of an ‘international drainage basin’ should be the appropriate basis for their study. Some states objected to the concept, arguing that it could result in regulation not only of the use of the water, but also of the land territory. 110 Ultimately, the expression ‘international watercourse’ was chosen by the ILC and supported by states. However, leading academics refute the argument that the concept ‘international watercourse’ is less expansive than ‘international drainage basin’, stating that Art 1(1) of the UN Convention ‘applies to uses of international watercourses and of their waters for purposes other than navigation and to measures of protection, preservation and management related to the uses of those watercourses and their waters’.111 This means that the Convention indirectly applies to land-based activities taking place within a river basin to the extent that such activities might be relevant for the use, protection, and management of an international watercourse.112
See Section 2.2 for an example of where an activity carried out within the drainage basin pollutes the international watercourse.
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