Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v. Nicaragua) and Construction of a Road in Costa Rica along the San Juan River (Nicaragua v. Costa Rica)

The San Juan de Nicaragua River belonged to Nicaragua (plaintiff) and marked the country’s boundary with Costa Rica (defendant). Costa Rica built a road on its side of the river. Over 100 kilometers of the road was within 5 to 100 meters of the river, and part of the construction involved deforesting land next to the river. Nicaragua filed a claim against Costa Rica with the International Court of Justice, arguing that Costa Rica had violated its: (1) procedural and substantive obligations under customary international law not to cause significant transboundary harm to Nicaragua, (2) obligations under customary international law to respect Nicaragua’s territorial integrity, and (3) obligations under a treaty to protect the environment. Costa Rica claimed that it had assessed the road’s environmental impact on the river before it began construction and determined that the only genuine environmental risk was a relatively small amount of sediment runoff. However, Costa Rica’s only evidence indicated that it had conducted this assessment after it had started construction rather than before. Costa Rica also submitted evidence that the road’s construction had not significantly harmed the river’s ecosystem or water quality. The court consolidated the case with separate claims brought by Costa Rica against Nicaragua about transboundary harm. The court considered the merits of Nicaragua’s claims.