International Waters Explained: What States Can Do on the High Seas

Introduction

International waters are maritime areas beyond the territorial sovereignty of individual states, but they are not places where national laws and international legal obligations cease to apply. The expression has no single formal definition under the United Nations Convention on the Law of the Sea (UNCLOS). It is commonly used to describe waters beyond a state's territorial sea, although the legally defined high seas generally begin beyond the exclusive economic zones of coastal states.

No state may claim sovereignty over the high seas. All states, including landlocked countries, enjoy recognized freedoms of navigation, overflight, fishing, scientific research, and other lawful maritime activities. These freedoms are subject to international law, which also regulates the operation of ships, the conservation of marine resources, and the circumstances in which states may intervene against foreign vessels (UNCLOS, 1982, arts. 87–90).

The distinction between freedom of navigation and freedom from legal authority is fundamental. A merchant vessel sailing thousands of miles from the nearest coast ordinarily remains subject to the jurisdiction of its flag state. A foreign warship cannot board it merely because it suspects unlawful conduct, although specific exceptions permit intervention. Understanding what states can do in international waters requires examining the maritime zone, the nationality and status of the vessel, the activity involved, and the legal basis for exercising jurisdiction.

1. Where International Waters Begin

The legal status of maritime waters depends on their relationship to coastal territory and the boundaries established under the law of the sea. UNCLOS distinguishes internal waters, territorial seas, contiguous zones, exclusive economic zones, and the high seas. Each category establishes different rights and obligations for coastal states and foreign vessels.

The principal distinction concerns sovereignty. A coastal state exercises sovereignty over its territorial sea, subject to the rights of foreign vessels and other limitations established by international law. Beyond that area, its authority is more restricted and depends on specifically recognized legal rights rather than general territorial control.

Maritime zones are measured from legally established baselines, normally corresponding to the low-water line along the coast. The distances established by UNCLOS represent maximum entitlements rather than guarantees that every state possesses uninterrupted maritime jurisdiction to those limits. Geography, overlapping coastal entitlements, and maritime delimitation agreements may affect the actual boundaries.

1.1 The 12-Mile Limit and the 200-Mile EEZ

Under UNCLOS Article 3, a coastal state may establish a territorial sea extending up to 12 nautical miles from its baselines. Its sovereignty extends to the waters, seabed, subsoil, and airspace within that zone. Foreign ships generally enjoy the right of innocent passage, but the coastal state retains substantial authority over navigation, security, and other activities, subject to the Convention's restrictions.

The contiguous zone may extend up to 24 nautical miles from the baselines. Article 33 permits the coastal state to exercise the control necessary to prevent infringements of its customs, fiscal, immigration, and sanitary laws within its territory or territorial sea, and to punish infringements committed there. This does not create another area of full territorial sovereignty.

Farther offshore, the exclusive economic zone may extend up to 200 nautical miles from the baselines. The coastal state enjoys sovereign rights concerning natural resources and specified jurisdiction over artificial installations, marine scientific research, and environmental protection. Other states retain freedom of navigation, overflight, and related lawful uses under Article 58.

Consequently, waters beyond the 12-nautical-mile territorial sea are not automatically high seas. A foreign merchant vessel may navigate through another state's EEZ without generally requiring coastal-state permission, but it cannot lawfully exploit that state's fisheries without complying with the applicable authorization and conservation requirements.

1.2 The High Seas and the Continental Shelf

Article 86 defines the scope of the high seas regime by excluding waters within a state's exclusive economic zone, territorial sea, internal waters, or archipelagic waters. Where a coastal state has established an EEZ extending to the maximum permitted breadth, the high seas begin beyond 200 nautical miles from its baselines. Their location may differ where no EEZ exists or where geography produces a different configuration of maritime zones.

The legal position becomes more complicated when the seabed is considered. Under Article 76, a coastal state's continental shelf may extend beyond 200 nautical miles if the Convention's conditions are satisfied. The state may possess exclusive rights over the natural resources of that seabed without acquiring sovereignty or equivalent jurisdiction over the high seas waters above it. Article 78 expressly preserves the legal status of the superjacent waters and airspace.

Beyond the limits of national continental shelf jurisdiction lies the international seabed Area. UNCLOS Article 136 designates the Area and its resources as the common heritage of mankind, with mineral-resource activities governed through the international regime established under Part XI. The International Seabed Authority administers that regime.

The separation between the water column and the seabed has practical consequences. A ship may exercise freedom of navigation above an extended continental shelf, but that freedom does not authorize it to exploit the coastal state's seabed resources. Equally, the presence of high seas waters above the international seabed Area does not entitle individual states to appropriate seabed minerals outside the applicable international system.

2. What States Can Do on the High Seas

UNCLOS Article 87 establishes the principle of freedom of the high seas. These waters are open to all states, regardless of geographical location or access to the coast. The Convention identifies six principal freedoms: navigation, overflight, laying submarine cables and pipelines, constructing installations permitted under international law, fishing, and scientific research. The enumeration is not exhaustive, but other activities must also comply with applicable international law.

Freedom of the high seas operates alongside the principle of nonappropriation. Article 89 prohibits states from subjecting any part of the high seas to their sovereignty. A state cannot lawfully convert an area of open ocean into national territory by occupying it, maintaining a permanent naval presence, or asserting exclusive control over international shipping routes.

These freedoms are subject to the obligation of due regard under Article 87(2). States must consider the interests of others exercising high seas freedoms and the rights recognized concerning activities in the international seabed Area. Additional restrictions arise under other UNCLOS provisions, specialized treaties, and customary international law. UNCLOS binds its parties as a treaty, while applicable customary rules may also bind states that have not joined the Convention.

2.1 Freedom of Navigation, Overflight, and Naval Operations

Freedom of navigation permits states to operate ships on the high seas without obtaining permission from coastal governments. Article 90 expressly recognizes the right of coastal and landlocked states to sail vessels flying their flags. Commercial shipping consequently operates through a legal system that protects access to international maritime routes while assigning responsibility for vessels primarily to their flag states.

Freedom of overflight allows aircraft to operate above the high seas without entering another state's sovereign airspace. Coastal sovereignty extends to the airspace above the territorial sea but not to airspace above the high seas. International aviation rules remain applicable, and the absence of territorial sovereignty does not eliminate obligations concerning aviation safety.

Naval vessels also benefit from freedom of navigation. States may conduct patrols, military exercises, surveillance operations, and other lawful activities on the high seas. UNCLOS Article 88 reserves these waters for peaceful purposes, while Article 301 requires states to refrain from threats or uses of force inconsistent with the principles of international law embodied in the United Nations Charter.

Neither provision establishes a general prohibition of military activity at sea. Naval exercises and deployments are not inherently unlawful, although their conduct must respect applicable rules concerning the use of force, the rights of other states, and maritime safety.

Military operations within another state's EEZ present a more contested question. Some coastal states maintain that certain foreign military exercises require prior consent, while major maritime powers generally defend broader operational freedoms under UNCLOS Article 58. The disagreement concerns the relationship between coastal-state rights and foreign military activities within the EEZ. It does not establish territorial sovereignty over that zone or alter the prohibition on sovereignty claims over the high seas.

2.2 Fishing, Scientific Research, and Submarine Cables

States may fish on the high seas, subject to conservation duties and applicable international agreements. The freedom recognized under Article 87 does not authorize practices that violate binding conservation measures. States retain responsibility for regulating fishing vessels flying their flags, while international cooperation is necessary to manage stocks that move across maritime boundaries.

Marine scientific research is another recognized freedom, but its legal conditions depend on where the research occurs and what it involves. UNCLOS Article 257 recognizes the right of states and competent international organizations to conduct marine scientific research in the water column beyond the limits of the EEZ. Research in those waters does not become subject to general coastal-state authorization merely because the seabed underneath forms part of an extended continental shelf.

Research directed at a coastal state's continental shelf is governed differently. Article 246 generally requires coastal-state consent for marine scientific research on the shelf, although states must normally grant consent for qualifying peaceful research projects. The Convention also restricts the circumstances in which consent may be withheld.

Under Article 246(6), a coastal state may not rely on the resource-related ground in Article 246(5)(a) to withhold consent for research beyond 200 nautical miles, except within specific areas that it has publicly designated. Such designations concern areas where exploitation or detailed exploratory operations are occurring or will occur within a reasonable period. The coastal state must give reasonable notice of the designation and any modifications, although it is not required to disclose details of the operations.

These distinctions preserve scientific freedoms in the water column while protecting legally recognized seabed rights. Research involving drilling, installations, or other activities directly affecting continental shelf interests may engage conditions that do not apply to ordinary water-column research. Environmental obligations remain relevant in both situations.

Submarine cables and pipelines illustrate the importance of shared maritime access. Article 112 recognizes the right of states to lay cables and pipelines on the bed of the high seas beyond the continental shelf, while Articles 113–115 address their protection and certain questions of liability. Where cables cross a coastal state's continental shelf, Article 79 establishes additional conditions concerning the respective rights of the coastal state and other states.

Article 87 also recognizes freedom to construct artificial islands and other installations permitted under international law, subject to the relevant continental-shelf provisions. Such structures do not automatically acquire the legal status of islands or generate new maritime zones. Their legality depends on their location, purpose, and relationship with existing jurisdictional rights.

3. Flag State Jurisdiction and the Law Aboard Ships

A vessel operating on the high seas does not become legally detached from every state. Under UNCLOS Article 91, ships possess the nationality of the state whose flag they are entitled to fly. The flag state establishes the conditions for registration and grants the right to use its national flag. Article 92 provides that ships ordinarily sail under one flag and are subject to that state's exclusive jurisdiction on the high seas, except in cases expressly provided for in international treaties or UNCLOS itself.

Flag-state jurisdiction supplies the principal legal connection between vessels and national authority. A ship registered in Panama, for example, generally remains subject to Panamanian jurisdiction while navigating the Atlantic or Pacific high seas, even when its crew members and cargo owners possess different nationalities. This nationality-based connection is one application of the broader principles of jurisdiction in international law.

Registration also carries responsibilities. Article 94 requires flag states to exercise effective jurisdiction and control over ships in administrative, technical, and social matters. These duties include measures concerning seaworthiness, equipment, crew qualifications, labor conditions, and maritime safety. Article 98 separately requires states to oblige masters of ships flying their flags to assist persons in distress at sea, subject to the conditions specified in that provision.

Article 91 requires a genuine link between a vessel and its flag state. The International Tribunal for the Law of the Sea examined this requirement in M/V Saiga (No. 2) (Saint Vincent and the Grenadines v. Guinea), explaining that its purpose is to secure more effective implementation of flag-state duties. A third state cannot automatically challenge a ship's nationality merely because it considers the connection between the vessel and its flag state insufficient (ITLOS, 1999, paras. 75–88).

The position differs for vessels without nationality or ships that use multiple flags according to convenience. Article 92(2) provides that a vessel sailing under the flags of two or more states and using them interchangeably cannot claim either nationality against another state and may be assimilated to a ship without nationality. Statelessness may justify the exercise of the right of visit, but it does not independently establish an unrestricted authority to arrest everyone aboard or seize the vessel for any suspected offense.

Warships and government vessels used exclusively for noncommercial service possess additional protection. Articles 95 and 96 recognize their complete immunity from the jurisdiction of states other than their flag states on the high seas. That immunity must be distinguished from the position of ordinary commercial vessels, which may be subject to recognized boarding and enforcement exceptions.

4. When States May Stop or Board Foreign Ships

The general principle of flag-state jurisdiction restricts the ability of other states to exercise coercive authority over foreign vessels. A government cannot ordinarily order a foreign merchant ship to stop, inspect its cargo, or arrest its crew on the high seas simply because the vessel is within the reach of its naval forces. Intervention requires a recognized legal basis.

International maritime law distinguishes several forms of intervention. Verifying a vessel's nationality is different from searching its cargo, while boarding for inspection does not necessarily authorize detention or seizure. Each measure must remain within the authority granted by the applicable legal rule.

These distinctions reflect the wider limits of enforcement jurisdiction in international law. A state may possess legitimate interests in suppressing piracy, trafficking, or unlawful fishing without having unrestricted authority to enforce its domestic laws against foreign vessels. UNCLOS establishes particular exceptions, supplemented by treaty-based cooperation, flag-state authorization, and exceptional decisions of the United Nations Security Council.

4.1 The Right of Visit Under UNCLOS Article 110

The right of visit is one of the clearest exceptions to exclusive flag-state jurisdiction. UNCLOS Article 110 permits a warship encountering a foreign vessel on the high seas to exercise a limited right of boarding where reasonable grounds exist for suspecting particular activities or circumstances. Ships entitled to complete immunity under Articles 95 and 96 are excluded from the ordinary application of this power.

Article 110 identifies five grounds. They concern suspected piracy, involvement in the slave trade, unauthorized broadcasting where the warship's flag state possesses jurisdiction under Article 109, absence of nationality, and cases in which a vessel appears foreign but actually possesses the nationality of the intervening warship. The right does not extend automatically to every suspected criminal offense.

The procedure begins with verification of the vessel's right to fly its flag. A warship may dispatch a boat commanded by an officer to examine the suspected vessel's documents. If suspicion remains after that examination, further inspection on board may be undertaken with the consideration required by Article 110(2). Military aircraft and other duly authorized government vessels or aircraft may also exercise the relevant powers under the conditions established by the Convention.

Article 110(3) provides for compensation where suspicions prove unfounded and the boarded vessel has committed no act justifying them. The compensation covers loss or damage sustained as a result of the inspection. This safeguard protects lawful navigation from unjustified interference.

The right of visit must also be distinguished from authority to seize property or prosecute individuals. Establishing a ground for boarding does not invariably establish a separate power of arrest. In cases involving unauthorized broadcasting, Article 109 contains additional jurisdictional rules. Other enforcement powers may arise under the piracy provisions or specialized international agreements.

4.2 Coastal-State Enforcement and Hot Pursuit

Coastal states possess certain enforcement powers beyond their territorial seas, particularly within their exclusive economic zones. UNCLOS Article 73 permits a coastal state to board, inspect, arrest, and institute judicial proceedings against foreign fishing vessels where necessary to ensure compliance with fisheries laws adopted consistently with the Convention.

These powers are limited by safeguards. Arrested vessels and crews must be promptly released upon the posting of reasonable bond or other security. Unless the states concerned agree otherwise, penalties for fisheries violations in the EEZ may not include imprisonment or other forms of corporal punishment. Article 73 also requires prompt notification to the flag state of enforcement action and subsequent penalties.

Marine pollution is governed by separate rules. Article 220 authorizes specified coastal-state measures against foreign vessels in the territorial sea and EEZ, subject to conditions that vary with the seriousness of the suspected violation, the available evidence, and its consequences. Environmental jurisdiction does not give a coastal state unrestricted power to inspect every passing ship.

The right of hot pursuit under Article 111 permits a coastal state to continue certain lawful enforcement operations beyond the maritime zone where the suspected violation occurred. Pursuit must begin when the foreign vessel, or another craft satisfying the Convention's relevant conditions, is within the zone where the coastal state possesses the applicable enforcement authority. A visual or auditory signal to stop must be given at a distance enabling it to be seen or heard, and pursuit must remain uninterrupted.

Different geographical conditions apply to pursuit initiated in territorial waters, the contiguous zone, the EEZ, or areas where continental-shelf rights are engaged. The pursuit ends when the vessel enters the territorial sea of its own state or a third state. It cannot be initiated against a foreign vessel already on the high seas merely because a coastal state subsequently suspects that an offense occurred within its jurisdiction.

Article 111(5) also restricts the vessels and aircraft entitled to undertake hot pursuit. The power may be exercised only by warships or military aircraft, or by other ships or aircraft clearly marked and identifiable as being on government service and authorized for that purpose. A privately operated vessel does not acquire the public enforcement powers associated with hot pursuit merely because it assists a coastal state.

In M/V Saiga (No. 2), the International Tribunal for the Law of the Sea held that the conditions governing hot pursuit are cumulative and found that Guinea had failed to satisfy several of them. The Tribunal also condemned the excessive force used against the vessel, reinforcing the requirement that maritime enforcement respect necessity, reasonableness, and the safety of those aboard (ITLOS, 1999, paras. 146–159).

4.3 Treaty-Based Boarding and Flag-State Authorization

Specialized treaties establish additional procedures for international cooperation against maritime offenses. These agreements do not abolish flag-state jurisdiction. Instead, they define the conditions under which other states may obtain authorization to inspect vessels or undertake specified enforcement measures.

Drug trafficking illustrates the distinction. UNCLOS Article 108 requires cooperation in suppressing illicit traffic in narcotic drugs and psychotropic substances by ships on the high seas in violation of international conventions. That obligation does not independently grant every state unrestricted authority to board foreign-flagged ships suspected of carrying drugs.

Article 17 of the 1988 United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances establishes more specific arrangements. Where a party reasonably suspects that a vessel flying another party's flag is engaged in illicit traffic, it may seek confirmation of registration and request authorization from the flag state. The flag state may permit boarding, searching, and appropriate subsequent action, subject to the authorization's terms and the Convention's safeguards (United Nations, 1988, art. 17).

The 2005 Protocol to the Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation introduced Article 8bis, establishing boarding procedures in connection with specified maritime offenses. Flag-state authorization remains central, although the Protocol permits parties to provide certain forms of advance consent through notifications. The procedures also include safeguards concerning safety, human dignity, and the treatment of persons aboard.

The 1995 United Nations Fish Stocks Agreement creates a different mechanism. Under Article 21, a state party participating in a relevant regional fisheries management organization or arrangement may, through duly authorized inspectors, board and inspect fishing vessels flying the flags of other parties to the Agreement in the high seas area concerned. This may apply even when the inspected vessel's flag state does not belong to the particular regional arrangement.

The authority is limited to the purposes and conditions established by the Agreement, including the conservation and management measures concerning straddling and highly migratory fish stocks. Article 22 establishes further inspection procedures and safeguards. These provisions do not create an unrestricted fisheries-policing power against vessels of states that are not parties to the Agreement.

The United Nations Security Council may also authorize maritime inspections in exceptional circumstances. Resolution 2292 (2016), adopted under Chapter VII of the UN Charter, authorized specified inspections of vessels on the high seas off Libya suspected of transporting arms or related materiel in violation of the applicable embargo. The authorization was initially limited to 12 months and required good-faith efforts to obtain flag-state consent before inspection.

The Council expressly preserved the general principle of exclusive flag-state jurisdiction outside the circumstances covered by the resolution. It also stated that the authorization did not establish customary international law (UN Security Council, 2016, para. 9). The resolution illustrates a distinct source of maritime enforcement authority without creating a permanent or universal exception to the law of the sea.

5. Crimes, Arrests, and Prosecution at Sea

Criminal activity on the high seas may be subject to national and international law even when it occurs beyond territorial sovereignty. The decisive issue is which state possesses jurisdiction over the conduct and whether it has legal authority to investigate, arrest, or prosecute the persons involved. Maritime location alone does not determine whether an offense can be punished.

International law distinguishes three forms of jurisdiction. Prescriptive jurisdiction concerns the authority to make laws applicable to particular conduct. Adjudicative jurisdiction concerns the competence of courts to hear cases and determine legal responsibility. Enforcement jurisdiction concerns coercive measures such as boarding, arrest, detention, and seizure. These powers may belong to different states in connection with the same incident.

A state may possess a legitimate basis for prosecuting an offense committed aboard a foreign vessel without possessing an independent right to board that vessel on the high seas. Flag-state jurisdiction remains the general rule for maritime enforcement, while nationality, particular treaties, and recognized exceptions may establish additional legal connections.

The exercise of maritime enforcement powers also remains subject to applicable international human-rights obligations. A lawful basis for intercepting a vessel does not automatically authorize indefinite detention, unlawful removal, or treatment incompatible with the rights of those aboard.

The European Court of Human Rights addressed this distinction in Hirsi Jamaa and Others v. Italy (2012). Italian authorities intercepted migrants on the high seas, transferred them onto Italian military vessels, and returned them to Libya. The Grand Chamber held that the individuals were under Italy's continuous and exclusive control during the operation and consequently fell within Italian jurisdiction for purposes of the European Convention on Human Rights (ECtHR, 2012, paras. 76–82).

The Court separately found that returning the applicants to Libya exposed them to a real risk of treatment prohibited by Article 3. It also found a violation of Article 3 arising from the risk of onward repatriation to Somalia or Eritrea. These conclusions rested on the conditions and risks established in the particular case (ECtHR, 2012, paras. 137–138 and 158).

The absence of any individual examination of the applicants' circumstances led the Court to find a violation of the prohibition of collective expulsion under Article 4 of Protocol No. 4. It also found a violation of Article 13, read together with Article 3 and Article 4 of Protocol No. 4, because the applicants lacked an effective remedy before their removal (ECtHR, 2012, paras. 185–186 and 207).

The judgment established that Italy could not avoid its Convention obligations by characterizing the operation as maritime rescue or relying on the fact that the interception occurred outside its territory. The decision concerns obligations under the European Convention and cannot automatically be treated as a universal jurisdictional test under every human-rights treaty.

It nevertheless demonstrates that state control exercised over individuals at sea may engage duties concerning humane treatment, effective remedies, and non-refoulement. The legal basis for maritime interception and the lawfulness of subsequent detention, treatment, or removal must be assessed separately.

5.1 Piracy and Universal Jurisdiction

Piracy constitutes one of the principal exceptions to ordinary flag-state jurisdiction. Under UNCLOS Article 101, the definition includes specified illegal acts of violence, detention, or depredation committed for private ends by the crew or passengers of a private ship or aircraft and directed against another ship, aircraft, or persons or property aboard it on the high seas. Article 101(a)(ii) separately covers conduct against ships, aircraft, persons, or property in places outside the jurisdiction of any state.

The definition also includes specified acts of voluntary participation and intentional facilitation. Article 102 extends the piracy rules to acts committed by warships or government ships or aircraft whose crews have mutinied and taken control. These provisions preserve the legally defined character of piracy rather than treating every serious maritime offense as equivalent.

The geographical distinction is essential. Violence against a ship within a state's territorial sea generally falls outside the definition of piracy in Article 101, although it may constitute armed robbery against ships or another offense under applicable law. The piracy provisions also apply within the EEZ through Article 58(2), insofar as they are compatible with the EEZ regime.

Article 100 requires states to cooperate to the fullest possible extent in repressing piracy. Article 105 permits states to seize pirate ships or aircraft on the high seas or in other places outside the jurisdiction of any state, arrest persons aboard, and seize property. The courts of the seizing state may determine penalties and decide what happens to seized vessels or property, subject to the rights of third parties acting in good faith.

These exceptional powers explain the association between piracy under international law and universal jurisdiction. Their exercise remains subject to the Convention's conditions, including Article 107 concerning the government vessels and aircraft authorized to conduct seizures.

Article 106 provides an additional safeguard. Where a ship or aircraft has been seized on suspicion of piracy without adequate grounds, the seizing state is liable to the state of the vessel's nationality for resulting loss or damage. The existence of suspicion sufficient to justify an initial visit cannot automatically be equated with the legal justification required for every subsequent coercive measure.

Universal jurisdiction over piracy also does not dispense with applicable criminal legislation, evidentiary requirements, and lawful judicial proceedings. Article 105 permits the courts of the seizing state to determine penalties; it does not establish that every piracy suspect may be punished without regard to national criminal law and procedural protections.

5.2 Criminal Acts, Collisions, and National Jurisdiction

Crimes committed aboard merchant vessels on the high seas may engage several national legal systems. The flag state ordinarily possesses jurisdiction over the vessel, while other states may claim prescriptive or adjudicative jurisdiction where a recognized legal connection exists, such as the nationality of an offender or victim. Whether those claims can be exercised depends on applicable international law and domestic legislation.

Maritime collisions are governed by a particular rule. UNCLOS Article 97(1) provides that penal or disciplinary proceedings arising from a collision or another incident of navigation on the high seas, involving the responsibility of a master or another person in the service of the ship, may be instituted only before the relevant authorities of the flag state or the state of nationality of the person concerned.

Article 97(2) establishes a separate rule concerning professional certificates. In disciplinary matters, only the state that issued a master's certificate, certificate of competence, or license may order its withdrawal, following due legal process, even where the holder possesses another nationality. Article 97(3) further provides that only the flag state may order the arrest or detention of the ship, including for investigative purposes.

The historical significance of these restrictions is connected to the S.S. Lotus case. In 1927, the Permanent Court of International Justice rejected France's contention that Turkey had violated international law by prosecuting a French officer following a collision on the high seas. The subsequent development of conventional law, including the 1952 Brussels Convention concerning penal jurisdiction in matters of collision and other navigational incidents, established more restrictive rules.

Article 97 reflects that later legal development. The Lotus judgment cannot be treated as unrestricted contemporary authorization for criminal prosecution or enforcement in collision cases governed by the Convention. Nor does Article 97 necessarily determine the jurisdictional position of offenses unrelated to collisions or other incidents of navigation.

Jurisdiction may also change when a commercial vessel enters a foreign port. Port states ordinarily exercise territorial authority over vessels voluntarily entering their internal waters, subject to applicable international rules, immunities, and jurisdictional limitations. Port entry may create opportunities for investigation or enforcement that were unavailable while the vessel remained on the high seas. It does not retroactively establish that a foreign state possessed an unrestricted right to intercept the ship offshore.

6. Conservation and Environmental Duties on the High Seas

The freedoms of the high seas coexist with international obligations concerning conservation, environmental protection, and the sustainable use of marine resources. Fishing, scientific research, navigation, and other maritime activities may affect ecosystems extending across national boundaries. Their regulation frequently depends on cooperation among states rather than the territorial authority of one government.

UNCLOS addresses these questions through general obligations and specialized rules. States retain rights to use the high seas, but they must exercise those rights consistently with applicable conservation duties, environmental provisions, and agreements governing particular activities. The freedom recognized under Article 87 cannot be interpreted in isolation from the Convention's other obligations.

Implementation presents a distinct difficulty. Flag states bear substantial responsibility for ensuring compliance by their vessels, while regional organizations and specialized international agreements establish additional conservation and monitoring arrangements. The absence of territorial sovereignty makes international cooperation particularly significant, although it does not diminish the binding character of obligations accepted under the relevant treaties.

6.1 High Seas Fishing and Conservation Obligations

UNCLOS Article 116 recognizes the right of states to engage in fishing on the high seas, subject to treaty obligations and the qualifications established by the Convention. Articles 117 and 118 require states to adopt or cooperate in conservation measures for living resources and to cooperate with other states in their conservation and management.

Article 119 addresses the determination of allowable catches and other conservation measures based on the best scientific evidence available, together with relevant environmental and economic factors. The Convention also requires consideration of associated or dependent species and the exchange of relevant scientific information through appropriate international organizations.

High seas fisheries often involve stocks moving between exclusive economic zones and areas beyond national jurisdiction. The 1995 United Nations Fish Stocks Agreement develops rules concerning straddling and highly migratory fish stocks, including cooperation, conservation measures, monitoring, and enforcement. It imposes additional treaty obligations on its parties rather than creating identical obligations for every state independently of treaty participation.

Regional fisheries management organizations provide institutional mechanisms for adopting conservation measures and coordinating compliance. Their effectiveness depends on the legal powers established by the relevant arrangements, participation by fishing states, and implementation through national authorities. Measures adopted within these organizations do not automatically bind every nonparticipating state merely because they concern the high seas.

The legal distinction remains between access to the high seas and entitlement to exploit resources without restriction. A fishing vessel may navigate freely through an ocean area while remaining subject to catch limits, reporting obligations, gear restrictions, or other applicable conservation requirements. Where a vessel enters an EEZ, coastal-state resource jurisdiction supplies an additional and different legal basis for regulation.

6.2 Marine Pollution and the BBNJ Agreement

Environmental protection imposes obligations extending beyond national maritime zones. UNCLOS Article 192 establishes a general duty to protect and preserve the marine environment. Article 194 requires states to take the measures necessary to prevent, reduce, and control marine pollution from any source, using the best practicable means at their disposal and in accordance with their capabilities. These duties operate alongside more specific provisions and applicable international agreements.

Pollution from ships, dumping, and other activities is subject to specialized regulation. The International Convention for the Prevention of Pollution from Ships (MARPOL) establishes international standards addressing several categories of vessel-source pollution. The legal treatment of marine plastic pollution also illustrates how environmental harm at sea can engage obligations concerning maritime operations and pollution originating on land.

The conservation regime has developed further through the Agreement on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction, commonly called the BBNJ Agreement. Adopted on June 19, 2023, the Agreement entered into force on January 17, 2026, becoming the third implementing agreement under UNCLOS.

The BBNJ Agreement addresses marine genetic resources and benefit-sharing, area-based management tools including marine protected areas, environmental impact assessments, and capacity-building and marine technology transfer. It establishes arrangements for cooperation and decision-making concerning marine biodiversity in areas beyond national jurisdiction, including the high seas and the international seabed Area.

Its geographical scope does not mean that every maritime activity falls under identical obligations. Article 4 excludes warships, military aircraft, and naval auxiliaries from the Agreement. Other vessels or aircraft owned or operated by a party and used exclusively for government noncommercial service are also excluded, except in relation to Part II concerning marine genetic resources.

That exception is further qualified by Article 10(3). The obligations of Part II do not apply to a party's military activities, including military activities undertaken by government vessels and aircraft engaged in noncommercial service. The same provision confirms that the obligations concerning the utilization of marine genetic resources and digital sequence information apply to a party's nonmilitary activities.

Article 4 also requires parties to adopt appropriate measures to ensure that the relevant government vessels and aircraft act consistently with the Agreement as far as reasonable and practicable, without impairing their operations or operational capabilities. These provisions distinguish military activities from nonmilitary government activities while preserving the specific exemptions established by the treaty.

Article 5 governs the relationship between the BBNJ Agreement, UNCLOS, and other international institutions. It requires the Agreement to be interpreted and applied consistently with UNCLOS and in a manner that does not undermine relevant legal instruments, frameworks, and global, regional, subregional, or sectoral bodies. The provision also promotes coherence and coordination among those arrangements.

The Agreement's entry into force does not mean that all its institutional mechanisms have already become operational. The first Conference of the Parties is scheduled to meet from January 11 to 22, 2027, at United Nations Headquarters in New York. That meeting will consider institutional and procedural arrangements needed for the Agreement's implementation.

The BBNJ Agreement creates binding obligations for its parties according to its terms, while particular conservation decisions and implementation mechanisms require further institutional action. It does not abolish high seas freedoms or replace the separate regimes governing fisheries, international shipping, or deep seabed mineral resources. Its legal contribution is the establishment of additional arrangements for conserving biodiversity in maritime areas beyond national jurisdiction.

Conclusion

International waters are not areas of unrestricted state action. On the high seas, all states enjoy recognized freedoms of navigation, overflight, fishing, scientific research, and other lawful maritime uses. No state may claim sovereignty over those waters, and none possesses a general entitlement to control foreign shipping merely because it has the capacity to do so.

The authority to regulate and enforce law at sea depends on the legal status of the maritime area and the persons or vessels involved. Flag-state jurisdiction supplies the principal basis for regulating ships on the high seas, while piracy, the right of visit, hot pursuit, treaty arrangements, and specific Security Council authorizations establish limited exceptions. Coastal states also retain particular rights within their exclusive economic zones and over their continental shelves without acquiring sovereignty over the high seas.

These jurisdictional powers remain subject to other applicable legal obligations, including those concerning maritime safety, human rights, conservation, and environmental protection. The central legal question is not simply whether an activity occurs beyond national territory, but which state possesses authority over it, what conduct that authority permits, and which international rules restrict its exercise.

References

Agreement for the Implementation of the Provisions of the United Nations Convention on the Law of the Sea of 10 December 1982 relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks (1995) Adopted 4 August 1995, entered into force 11 December 2001. 2167 UNTS 3.

Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (2023) Adopted 19 June 2023, entered into force 17 January 2026. United Nations document A/CONF.232/2023/4.

Charter of the United Nations (1945) Signed 26 June 1945, entered into force 24 October 1945. 1 UNTS XVI.

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