Rivers — Boundary rivers — Navigation — San Juan River forming boundary between Costa Rica and Nicaragua — 1858 Treaty between Costa Rica and Nicaragua — International border fixed on the Costa Rican bank of the river — Entire territory of the river within the sovereignty of Nicaragua — Right of navigation “con objetos de comercio” granted to Costa Rican vessels — Interpretation of treaty — Whether extending to carriage of passengers, including tourists — Navigation by members of Costa Rican riparian communities for purpose of everyday needs — Use of river by Costa Rican official vessels — Regulatory powers of Nicaragua

Treaties — Interpretation — Principles of interpretation — Vienna Convention on the Law of Treaties, 1969 — Whether terms in treaty of long duration to be given an evolving meaning — Treaty imposing restriction on sovereignty of State within its own territory — Whether justifying restrictive interpretation — 1858 Treaty between Costa Rica and Nicaragua regarding sovereignty over, and navigation on, the San Juan River

Sources of international law — Customary international law — Customary practices by riparian communities along border river — Whether capable of giving rise to customary law rights regarding navigation and subsistence fishing

International Court of Justice — Remedies — Presumption that State will comply with judgment of the Court — Whether appropriate to order future compliance