Rivers — International rivers — Freedom of navigation — Definition — Certificate facilitating cross-border navigation of the River Rhine — Restriction limiting issuance of certificates to nationals of certain countries — Whether constituting impediment to freedom of navigation — Revised Act Concerning Navigation of the Rhine (Act of Mannheim), 1868–1922

Sources of international law — General principles of law — Protest and acquiescence — Estoppel — Regulations issued by International River Commission pursuant to international treaty — Unilateral modification of regulations by party to treaty — Subsequent protest by other parties — The law of the Netherlands