|Two watercourse states are free to enter into an agreement which covers the whole or part of a watercourse, provided third watercourse states are not adversely affected ‘to a significant extent’. This test of what is to a ‘significant extent’ is an objective test which requires that the effect is one which can be established by objective evidence. Additionally, it must be shown that there is a real impairment of use.155 Additionally the term ‘significant’ is not used in the sense of ‘substantial’. What are to be avoided are localised agreements, or agreements concerning a particular project or use, which have a significant adverse effect upon third watercourse states – such an effect need not rise to the level of being substantial.156 The Arbitral Tribunal, in the award of the Lake Lanoux Arbitration, in which Spain insisted upon delivery of Lake Lanoux water through the original system, found that:
‘[…] thanks to the restitution effected by the devices described above, none of the guaranteed users will suffer in his enjoyment of the waters […]; at the lowest water level, the volume of the surplus waters of the Carol, at the boundary, will at no time suffer a diminution; In the absence of any assertion that Spanish interests were significantly affected in a tangible way, the tribunal held that Spain could not require maintenance of the natural flow of the waters’.157
The term ‘significant’ is a term that pervades many of the provisions of the Convention and as such is discussed further throughout this Guide as it applies to specific Articles and contexts.
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