Spain v. France (Lac Lanoux Arbitration)

France (defendant) planned to build a reservoir at Lake Lanoux to generate electricity, with a river running from the lake flowing downstream into Spain (plaintiff); to address any water loss Spain might suffer, France offered to construct an underground tunnel supplying an equivalent volume of water from other sources. Spain challenged the plan under the 1866 Treaty of Bayonne between the two countries, arguing France could not proceed with this kind of construction without a prior agreement between the nations, and an arbitral tribunal was convened to resolve the dispute.