Sovereignty at the Land-Sea Interface: Legal Regimes and Coastal Jurisdiction in Internal Waters

Under public international law, the world’s oceans are divided into distinct maritime zones, each defined by a specific balance between the sovereign rights of coastal states and the freedoms enjoyed by the international community. At the innermost edge of this legal structure lie internal waters. Encompassing ports, harbors, rivers, lakes, landward bays, and waters enclosed by straight baselines, internal waters represent the maritime spaces most intimately connected to a state's terrestrial domain.

Unlike the territorial sea, the exclusive economic zone (EEZ), or the high seas, internal waters are subject to the absolute and exclusive sovereignty of the coastal state. Within these waters, the legal presumption of international navigational freedom yields almost entirely to domestic jurisdiction. Understanding the legal regime of internal waters requires an analysis of how these areas are geographically defined, how coastal states exercise prescriptive and enforcement powers, and how international law accommodates exceptions such as force majeure and port state control.

Understanding the Legal Nature of Internal Waters

The foundational framework governing internal waters is codified in the 1982 United Nations Convention on the Law of the Sea (UNCLOS). Article 8(1) of UNCLOS establishes the primary definition: \"Except as provided in Part IV, waters on the landward side of the baseline of the territorial sea form part of the internal waters of the State.\"

This definition anchors internal waters to the concept of the baseline—the low-water line along the coast or the constructed straight lines from which the territorial sea and other maritime zones are measured. Because internal waters sit inside this baseline, international law treats them as an extension of the state's land territory. Sovereignty over these waters extends to the airspace above, the water column, the seabed, and the subsoil beneath.

Sovereignty over internal waters is absolute and territorial in nature. It differs fundamentally from the conditional sovereign rights exercised in the exclusive economic zone or on the continental shelf.

The primary consequence of this status is that foreign vessels do not enjoy an automatic right of innocent passage through internal waters. While foreign ships have a recognized right to traverse a coastal state's territorial sea without prior authorization—provided their passage is continuous, expeditious, and non-prejudicial to peace and good order—no such general right exists once a vessel crosses landward of the baseline.

The Delineation of Internal Waters: Baselines and Geography

Determining where internal waters begin requires understanding how maritime baselines are drawn. International law recognizes several geographic configurations that generate internal waters.

Normal Baselines vs. Straight Baselines

Under Article 5 of UNCLOS, the normal baseline for measuring the breadth of the territorial sea is the low-water line along the coast, as marked on large-scale charts officially recognized by the coastal state. Waters located landward of this low-water mark—such as domestic rivers, estuaries, and inland lakes—are naturally internal waters.

However, where the coastline is deeply indented or cut into, or where there is a fringe of islands along the coast in its immediate vicinity, a state may employ straight baselines under Article 7. When straight baselines are drawn connecting appropriate points on the coast, all waters enclosed between those baselines and the mainland automatically acquire the legal status of internal waters.

Bays, River Mouths, and Ports

Specific geographical features receive tailored legal treatment under UNCLOS:

• Bays: Under Article 10, a well-marked indentation qualifies as a legal bay if its area is as large as, or larger than, that of the semi-circle whose diameter is a line drawn across the mouth of that indentation. If the distance between the low-water marks of the natural entrance points does not exceed 24 nautical miles, a closing line may be drawn, enclosing the bay as internal waters. Historic bays, which rely on long-standing, continuous, and unchallenged exercises of state authority, represent an exception to the 24-mile mathematical rule.
• River Mouths: Article 9 specifies that if a river flows directly into the sea, the baseline is a straight line drawn across the mouth of the river between points on the low-water line of its banks.
• Ports and Roadsteads: Article 11 provides that the outermost permanent harbor works which form an integral part of the harbor system are regarded as forming part of the coast. Consequently, waters inside modern port facilities, breakwaters, and docks constitute internal waters. Roadsteads used for loading, unloading, and anchoring ships are subject to special regulatory controls, even if situated partly outside the normal baseline.

The Article 8(2) Exception for Innocent Passage

An important exception to the rule against innocent passage in internal waters is contained in Article 8(2) of UNCLOS. Where the establishment of a straight baseline under Article 7 has the effect of enclosing as internal waters areas which had not previously been considered as such, a right of innocent passage continues to exist in those specific waters. This provision prevents coastal states from using straight baseline systems to suddenly sever established international navigation routes.

The Scope of Coastal State Sovereignty

Because internal waters form part of the sovereign territory of the coastal state, the scope of national jurisdiction within these waters is comprehensive. The coastal state exercises three core legal powers:

1. Prescriptive Jurisdiction: The authority to enact legislation governing all activities within internal waters, including immigration, customs, fiscal matters, sanitary conditions, environmental protection, navigation safety, and resource exploitation.
2. Enforcement Jurisdiction: The power to arrest individuals, inspect vessels, seize property, and execute judicial process for violations of national laws committed within internal waters or ports.
3. Adjudicative Jurisdiction: The competency of domestic courts to hear civil and criminal cases arising from events occurring within these waters.

Access to Internal Waters and Ports: Rights, Conditions, and Exceptions

A central legal question regarding internal waters is whether foreign vessels possess a right of entry into maritime ports and internal waterways. The short answer under general international law is no; entry into internal waters is a privilege granted by the coastal state rather than an inherent international right.

Principles of Port Entry

In the landmark Nicaragua v. United States case (1986), the International Court of Justice (ICJ) affirmed that by virtue of its sovereignty, a coastal state enjoys the right to regulate or prohibit access to its ports. A state may choose to open its ports to foreign commercial shipping to facilitate trade, but it retains the legal authority to close those ports or condition access on compliance with specific domestic rules.

Coastal states frequently condition entry on compliance with technical standards, security clearances, prior notification protocols, and environmental criteria. For example, states may deny entry to vessels that fail to meet safety construction standards, lack proper liability insurance, or carry dangerous cargoes without authorization.

The Right of Distress and Force Majeure

The primary exception to a coastal state's right to exclude foreign vessels from internal waters is the long-established customary rule of distress (or force majeure). Under this principle, a foreign vessel facing an immediate threat to the life of those on board or the imminent destruction of the ship due to severe weather, structural failure, or extreme emergency has a right to seek refuge in a coastal state's internal waters or port.

When a ship enters internal waters under genuine conditions of distress:

• The coastal state must grant temporary access to secure life and safety.
• The vessel is generally exempt from local customs duties, entry fees, and administrative penalties arising solely from its unauthorized entry.
• The immunity granted under distress is temporary and limited strictly to what is necessary to alleviate the emergency.

Jurisdictional Allocation Over Foreign Vessels in Port

When a foreign vessel voluntarily enters a port or internal waters, it subjects itself to the territorial jurisdiction of the coastal state. However, international legal practice has developed practical distinctions regarding how domestic criminal and civil jurisdiction is exercised on board merchant ships.

Criminal Jurisdiction: The "Peace of the Port" Doctrine

In practice, coastal states distinguish between crimes that affect the broader peace and security of the coastal state and those that remain purely internal to the vessel.

Under the widely accepted "Peace of the Port" doctrine (often traced to French administrative law and Anglo-American legal tradition):

• Internal Discipline: Matters concerning only the internal order, discipline, or administration of the ship—such as minor disputes between crew members or routine internal employment issues—are generally left to the jurisdiction of the flag state's captain and consular officials.
• Disturbance of the Port: If an offense committed on board impacts the peace, safety, or good order of the port, or if the offense is severe (such as homicide, drug trafficking, or violent felony), the coastal state will step in and exercise its criminal jurisdiction.
• Assistance Requested: The coastal state will also exercise jurisdiction if the master of the ship or a diplomatic representative of the flag state formally requests local authority intervention.

Civil Jurisdiction and Maritime Claims

Coastal states possess full legal authority to exercise civil jurisdiction over foreign merchant vessels in port. This includes the power to arrest a vessel pursuant to judicial proceedings for maritime claims, such as salvage disputes, collision damages, unpaid crew wages, or unpaid port charges, subject to domestic law and international conventions governing ship arrest.

Sovereign Immunity for Warships and Government Vessels

A critical limitation on coastal state jurisdiction in internal waters applies to foreign warships and naval auxiliaries operating for non-commercial purposes. Under Article 32 of UNCLOS and customary international law, foreign warships enjoy complete sovereign immunity from local jurisdiction.

While a foreign warship must comply with the laws and regulations of the coastal state regarding navigation, anchoring, and environmental safety while in port, coastal state authorities may not board, inspect, arrest, or seize the vessel. If a warship fails to comply with port regulations, the coastal state's primary legal remedy is to order the vessel to leave its internal waters immediately.

Port State Jurisdiction and Environmental Enforcement

In modern maritime law, internal waters—specifically ports—serve as the vital legal nexus for enforcing international environmental and safety standards. This framework, known as Port State Control (PSC), empowers coastal states to inspect foreign vessels visiting their ports to ensure compliance with global conventions.

Enforcement under UNCLOS Part XII

Part XII of UNCLOS grants extensive powers to port states to protect the marine environment. Under Article 218, when a vessel is voluntarily within a port or at an off-shore terminal of a state, that state may undertake investigations and, where the evidence warrants, institute proceedings in respect of any discharge from that vessel outside its internal waters, territorial sea, or EEZ in violation of applicable international standards.

Furthermore, Article 220(1) authorizes the port state to initiate legal proceedings against vessels that have committed environmental violations within its territorial sea or EEZ once those vessels voluntarily enter internal waters or a port facility.

International Environmental Conventions

Port State Control regimes operate pursuant to key international instruments administered by the International Maritime Organization (IMO), including:

• MARPOL: The International Convention for the Prevention of Pollution from Ships, regulating operational and accidental oil spills, noxious liquids, sewage, garbage, and air emissions.
• SOLAS: The International Convention for the Safety of Life at Sea, covering vessel construction, equipment, and operational safety.
• STCW: The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers.
• Ballast Water Management Convention: Governing the discharge of ballast water to prevent the introduction of invasive aquatic species into fragile coastal ecosystems.

By making compliance with these international standards a condition of entry into internal waters, coastal states exercise immense leverage over global shipping safety without exceeding their geographical jurisdiction.

Internal Waters vs. Archipelagic Waters: Key Legal Distinctions

It is essential to distinguish internal waters from archipelagic waters, a distinct legal category created under Part IV of UNCLOS for archipelagic states such as Indonesia, the Philippines, and Fiji.

Under Article 47, an archipelagic state may draw straight archipelagic baselines joining the outermost points of the outermost islands and drying reefs. The waters enclosed within these baselines are designated as archipelagic waters.

While the archipelagic state exercises sovereignty over these waters, archipelagic waters are not internal waters. The critical legal distinctions include:

• Right of Passage: Foreign ships retain the right of innocent passage through archipelagic waters. Furthermore, foreign ships and aircraft enjoy the right of archipelagic sea lanes passage through designated sea lanes and air routes.
• Internal Waters within Archipelagic Waters: An archipelagic state may delineate actual internal waters within its archipelagic waters by drawing closing lines across river mouths, bays, and ports in accordance with Articles 9, 10, and 11.

Contemporary Challenges in the Regime of Internal Waters

The traditional legal rules governing internal waters face novel challenges as maritime technology, environmental imperatives, and geopolitical dynamics evolve.

Maritime Autonomous Surface Ships (MASS)

The development of uncrewed and autonomous merchant vessels presents complex questions for port state jurisdiction. Coastal states are currently evaluating how to enforce domestic entry requirements, pilotage mandates, and safety certifications on ships operating without onboard crews. Defining how the "Peace of the Port" doctrine applies when no human master is present aboard a vessel in internal waters requires updated domestic legislative frameworks.

Cybersecurity in Critical Port Infrastructure

Modern seaports are highly digitized networks integrating logistics, automated crane operations, and customs management. As physical ports become targets for cyber operations, states are increasingly framing port access requirements around compliance with national cyber defense standards. Denying port entry to vessels with unverified digital security protocols represents a modern extension of traditional state sovereignty in internal waters.

Decarbonization and Alternative Marine Fuels

As the international maritime sector transitions toward zero-carbon fuels—such as green ammonia, hydrogen, and advanced lithium battery systems—coastal states are enacting stringent regulatory requirements for foreign ships entering internal waters. Standardizing safety protocols for fueling and handling hazardous green fuels within densely populated port facilities remains an urgent legal priority for port authorities worldwide.

Conclusion

Internal waters represent the theoretical and practical apex of coastal state authority in international law. Positioned landward of the baseline, these waters are governed by the same comprehensive territorial sovereignty that applies to a state's land territory. Within this domain, foreign navigation is a privilege conditioned upon local laws rather than an automatic freedom.

Yet, the legal regime of internal waters is not absolute isolationism. Through legal doctrines such as force majeure entry rights, sovereign immunity for warships, and standardized Port State Control rules, international law maintains a delicate balance between the territorial authority of the coastal state and the operational needs of global maritime trade and diplomacy. As ocean usage expands, internal waters will remain the essential legal portal where international maritime standards meet national sovereignty.