The United Nations Convention on the Law of the Sea (UNCLOS) divides the world’s oceans into a series of legally distinct maritime zones, each conferring different rights and obligations on coastal states and other users of the sea. These zones balance two competing principles: the extension of coastal state jurisdiction and the preservation of the oceans as a shared domain for navigation, commerce, and security. Disputes over their interpretation and application have made maritime zones a persistent source of geopolitical tension.
Diagram of maritime zones under international law by the National Oceanic and Atmospheric Administration
The following sections describe each of these maritime zones in turn, beginning with internal waters and extending seaward through the territorial sea and exclusive economic zone to the high seas, outlining their legal status, spatial limits, and principal areas of controversy.
Internal Waters
Definition: Internal waters are maritime areas on the landward side of a coastal state’s baseline. They include ports, harbours, rivers, estuaries, and bays, and are legally treated as indistinguishable from land territory.
Spatial Scope: They extend from the coastline inland to the baseline used to measure the territorial sea. Where straight baselines are employed, large stretches of water that might otherwise be considered coastal seas can fall within internal waters.
Sovereignty and Legal Status: The coastal state exercises full sovereignty over its internal waters, equivalent to its authority on land. Unlike the territorial sea, there is no general right of innocent passage for foreign vessels. Entry is subject entirely to the consent of the coastal state, except where specific treaty obligations or longstanding usage apply.
Permitted and Restricted Activities: The coastal state has complete control over navigation, port access, customs, immigration, environmental regulation, and security. It may deny entry to foreign vessels, impose conditions on port calls, or detain ships under domestic law.
Foreign warships and government vessels typically require explicit permission to enter internal waters or ports, and port access is frequently used as a tool of diplomatic signalling or coercion.
Typical Controversies: Disputes often arise over the drawing of straight baselines, which can convert previously open waters into internal waters. Claims based on historic bays or historic title are also contentious, particularly where they restrict long-standing navigation routes. Denial of port access to foreign naval or commercial vessels can escalate into diplomatic disputes, especially during periods of heightened political tension.
Geopolitical Significance: Internal waters sit at the most sovereignty-sensitive end of maritime jurisdiction. Control over ports and harbours gives coastal states leverage over trade, naval logistics, and diplomatic engagement. Decisions to grant or deny access are closely watched signals of alignment, hostility, or coercive intent, making internal waters a quiet but powerful instrument of statecraft.
Neutral Ports in WW2
During the Second World War, access to ports and harbours became a recurring point of dispute between belligerent and neutral states. Between 1939 and 1945, countries such as Sweden and Spain imposed strict controls on entry to their ports, allowing some warships to enter under limited conditions while denying access to others.
Affected states protested selective treatment, but no legal mechanism existed to compel access. The outcome was acceptance in practice that ports and harbours fell entirely under coastal state authority. This approach carried into the post-war legal order and was later reflected in UNCLOS, which treats internal waters as fully subject to state control with no general right of passage.
Territorial Seas
Definition: The territorial sea is the maritime zone immediately adjacent to a coastal state’s land territory and is legally treated as an extension of that territory at sea. It forms the innermost layer of maritime jurisdiction under UNCLOS.
Spatial Scope: Territorial seas extend up to 12 nautical miles from the coastal baseline, usually measured from the low-water line along the coast.
Sovereignty and Legal Status: Within the territorial sea, the coastal state exercises full sovereignty over the water column, seabed, subsoil, and airspace above, comparable to its authority on land. This sovereignty is qualified by the right of innocent passage, which allows foreign vessels to transit the zone without prior authorisation, provided certain conditions are met.
Permitted and Restricted Activities: The coastal state controls natural resources, law enforcement, customs, immigration, and security within the territorial sea. It may adopt and enforce laws governing navigation, environmental protection, and public order.
Innocent passage by foreign vessels must be continuous and expeditious and must not threaten the peace, good order, or security of the coastal state. Activities such as weapons exercises, intelligence collection, or interference with communications are commonly cited as rendering passage non-innocent.
Typical Controversies: Disputes frequently arise over how innocent passage applies to warships, submarines, and vessels engaged in surveillance or intelligence gathering. Some coastal states require prior notification or consent for military vessels, while maritime powers reject such restrictions. Additional friction stems from excessive claims that extend territorial seas beyond the 12-nautical-mile limit or impose conditions inconsistent with UNCLOS.
Geopolitical Significance: The territorial sea is a frequent setting for naval encounters, freedom of navigation operations, and diplomatic protests. It is a key zone through which coastal states seek to limit foreign military presence close to their shores, while naval powers view it as a test case for the broader integrity of navigational rights at sea.
The Corfu Channel Incident
The Corfu Channel incident of 1946 brought the legal status of the territorial sea into focus. British warships transited the Corfu Channel without Albania’s consent and struck naval mines, causing significant loss of life. Albania claimed that its sovereignty had been violated, while the United Kingdom argued that it was entitled to pass through a strait used for international navigation.
The case was referred to the International Court of Justice, which held Albania responsible for failing to warn of the mines while recognising a right of passage for warships. The ruling influenced later codification of innocent passage and the treatment of international straits under UNCLOS.
Contiguous Zone
Definition: The contiguous zone is a maritime area beyond the territorial sea in which a coastal state may exercise limited control for specific enforcement purposes. It does not confer sovereignty, but extends certain regulatory powers beyond territorial waters.
Spatial Scope: The contiguous zone may extend up to 24 nautical miles from the coastal baseline, meaning it covers the area between 12 and 24 nautical miles from shore.
Legal Status: Within the contiguous zone, the coastal state does not enjoy full territorial authority. Instead, UNCLOS permits it to take necessary measures to prevent and punish infringements of its customs, fiscal, immigration, and sanitary laws committed within its territory or territorial sea.
Permitted and Restricted Activities: Coastal states may conduct inspections, surveillance, and enforcement actions related to the four specified legal categories. These powers are preventative and corrective in nature, aimed at stopping violations before they reach territorial waters or responding to offences already committed.
Other states retain freedoms of navigation and overflight. Military activities and commercial transit are generally unrestricted, provided they do not interfere with lawful enforcement actions.
Typical Controversies: Disputes arise when coastal states use the contiguous zone to justify broader security or military controls not explicitly authorised under UNCLOS. Expanded interpretations tied to counterterrorism, sanctions enforcement, or migration control have drawn objections from maritime powers. Questions also emerge over proportionality, particularly where interdictions resemble de facto territorial enforcement.
Geopolitical Significance: The contiguous zone functions as a legal buffer between sovereignty and the high seas. It is frequently used in efforts to manage irregular migration, smuggling, and public health risks, placing it at the intersection of maritime law enforcement and foreign policy. While less visible than other maritime zones, it plays a steady role in shaping how states extend authority seaward without formally expanding territorial claims.
Extending Enforcement Beyond the Coast
In the years following the Second World War, states increasingly intercepted vessels beyond their territorial seas to enforce customs and immigration laws. During the 1940s and 1950s, practices by countries such as the United States extended enforcement seaward without claiming full sovereignty. These actions were generally tolerated and did not provoke sustained legal challenges, despite exceeding traditional jurisdictional limits.
The absence of widespread objection contributed to the formal recognition of the contiguous zone in the 1958 Geneva Conventions and later in UNCLOS, which confined enforcement powers to a narrow set of regulatory purposes.
Exclusive Economic Zone (EEZ)
Definition: The exclusive economic zone is a maritime zone in which a coastal state holds sovereign rights for the purpose of exploring, exploiting, conserving, and managing natural resources in the water column, seabed, and subsoil. It represents a hybrid space combining coastal state resource control with continued freedoms for other states.
Spatial Scope: The EEZ extends up to 200 nautical miles from the coastal baseline, unless constrained by overlapping claims from neighbouring states.
Legal Status: Within the EEZ, the coastal state does not exercise full sovereignty. Its rights are limited to economic activities, environmental protection, marine scientific research regulation, and the construction of offshore installations. Other states retain freedoms of navigation and overflight, as well as the laying of submarine cables and pipelines.
Permitted and Restricted Activities: Coastal states control fisheries, offshore oil and gas development, renewable energy projects, and seabed resource management within the EEZ. They may enforce conservation measures, board vessels engaged in unlawful fishing, and regulate marine scientific research.
Foreign military vessels may transit and operate in EEZs, but this remains contested. Some states view military exercises and intelligence collection as permissible high-seas activities, while others argue that such operations threaten security and require consent.
Typical Controversies: The EEZ is the most contested maritime zone under UNCLOS. Overlapping EEZ claims are common, particularly in semi-enclosed seas. Disputes frequently arise over maritime boundary delimitation, fisheries enforcement, hydrocarbon licensing, and military activity. Competing interpretations of EEZ rights have led to vessel detentions, close naval encounters, and prolonged diplomatic disputes.
Geopolitical Significance: EEZs encompass the majority of commercially valuable offshore resources and sit at the centre of modern maritime competition. Control over EEZs affects food security, energy supply, and industrial strategy, while disagreements over permissible activities make them frequent sites of legal contestation and strategic signalling.
Cod Wars
The Cod Wars between Iceland and the United Kingdom from 1958 to 1976 centred on fisheries jurisdiction beyond established territorial limits. Iceland progressively extended its exclusive fishing zones and enforced them through arrests and the cutting of trawler nets, leading to repeated confrontations with British vessels.
The disputes escalated diplomatically but did not result in judicial settlement. The United Kingdom ultimately accepted Iceland’s expanded claims through bilateral agreements. These events fed into broader international acceptance of extended coastal resource rights and influenced the creation of the 200-nautical-mile EEZ under UNCLOS.
Continental Shelf
Definition: The continental shelf is the seabed and subsoil extending beyond a coastal state’s land territory to the outer edge of the continental margin. Under UNCLOS, it is a legal construct distinct from the water column above it and exists independently of whether a state declares it.
Spatial Scope: All coastal states are entitled to a continental shelf extending to 200 nautical miles from the baseline. Where the natural continental margin extends further, a state may claim an extended continental shelf beyond 200 nautical miles, subject to defined geological and geomorphological criteria.
Legal Status: Within the continental shelf, the coastal state holds exclusive sovereign rights over seabed and subsoil resources, including oil, gas, and mineral deposits. These rights do not depend on occupation or proclamation and do not affect the legal status of the waters above, which may remain part of the EEZ or the high seas.
Permitted and Restricted Activities: Coastal states may authorise drilling, seabed mining, and the construction of installations related to resource exploitation. They also regulate marine scientific research related to the shelf.
Other states retain the right to lay submarine cables and pipelines on the continental shelf, subject to reasonable coastal state conditions related to resource protection and environmental management.
Typical Controversies: Disputes arise over the delimitation of continental shelves between neighbouring states and over claims to extended shelves beyond 200 nautical miles. These claims are technically complex and often overlap, particularly in regions with broad continental margins. Tensions also emerge where seabed resource development intersects with cable routes or environmental concerns.
Geopolitical Significance: Continental shelf claims can substantially expand a state’s access to offshore hydrocarbons and strategic minerals, giving them long-term economic and security implications. In regions such as the Arctic and parts of the Atlantic and Indian Oceans, extended continental shelf submissions have become an increasingly significant weapon of long-term strategic competition, linking geology, law, and geopolitics in ways that can have significant territorial impact.
The Truman Proclamation
The modern legal concept of the continental shelf emerged with the 1945 Truman Proclamation, in which the United States asserted jurisdiction over seabed resources beyond its territorial sea. Other coastal states followed with similar claims, particularly as offshore oil exploration expanded.
While controversial, these assertions were not reversed through international litigation and gradually became accepted practice. The result was incorporation of seabed resource rights into the 1958 Continental Shelf Convention and their further development under UNCLOS, separating seabed entitlements from sovereignty over the waters above.
High Seas
Definition: The high seas are all parts of the ocean that lie beyond national jurisdiction. They begin beyond the outer limits of the exclusive economic zone or, where no EEZ is claimed, beyond the territorial sea. No state may claim sovereignty over any part of the high seas.
Spatial Scope: The high seas cover the majority of the world’s oceans, forming the largest single maritime space governed by UNCLOS.
Legal Status: The high seas are legally open to all states, whether coastal or landlocked. They are governed by a principle of freedom rather than jurisdiction, subject to shared rules intended to prevent abuse and manage common risks.
Permitted and Restricted Activities: All states enjoy freedoms of navigation and overflight on the high seas, as well as the right to lay submarine cables and pipelines, conduct fishing, and undertake scientific research. Naval operations are fully permitted, and military vessels may operate without coastal state consent.
Restrictions are limited but significant. States must cooperate to suppress piracy, slavery, unauthorised broadcasting, and illicit trafficking. Activities are also constrained by environmental obligations and emerging conservation regimes, particularly for fisheries and biodiversity beyond national jurisdiction.
Typical Controversies: Enforcement on the high seas is uneven, as jurisdiction generally rests with the flag state rather than the location of the activity. This has enabled illegal fishing, sanctions evasion, and environmental harm where flag-state control is weak or absent. Disputes also arise over the scope of military activity, intelligence collection, and interference with seabed infrastructure such as undersea cables.
Geopolitical Significance: The high seas function as the connective tissue of the global system, enabling trade, data flows, and military mobility. At the same time, they have become increasingly congested and contested, with major powers using naval presence and operational behaviour to signal resolve and shape norms. While UNCLOS defines the legal framework, outcomes on the high seas are just as heavily influenced by capacity, presence, and power as they are by the convention.
Cold War Naval Operations
Throughout the Cold War, the high seas served as a primary arena for naval operations by the United States and the Soviet Union. From the 1950s through the 1980s, submarines, surface vessels, and surveillance platforms operated globally, often in close proximity to one another.
These activities generated incidents and diplomatic protests but did not produce successful efforts to restrict military operations beyond national jurisdiction. The outcome was continued acceptance of broad navigational and operational freedoms on the high seas, later reflected in UNCLOS alongside parallel political agreements aimed at reducing risk.
The Area
Definition: “The Area” refers to the seabed, ocean floor, and subsoil beyond the limits of national jurisdiction. It lies outside all exclusive economic zones and continental shelf claims and is treated as a distinct legal space under UNCLOS.
Spatial Scope: The Area covers roughly half of the Earth’s surface, encompassing vast stretches of deep ocean beyond the reach of coastal state sovereignty.
Legal Status: UNCLOS designates the Area and its mineral resources as the common heritage of mankind. No state may claim sovereignty or sovereign rights over any part of it. Activities in the Area are carried out under international administration rather than national control, primarily through the International Seabed Authority.
Permitted and Restricted Activities: States and state-sponsored entities may conduct exploration and, potentially, exploitation of seabed minerals only with authorisation from the ISA. These activities are subject to contractual terms, environmental obligations, and benefit-sharing arrangements.
Scientific research is permitted, though distinctions between research and commercially relevant surveying have become increasingly blurred. Fishing and navigation are governed by high seas rules, as the Area concerns only the seabed and subsoil, not the water column above.
Typical Controversies: Disputes surrounding the Area focus less on boundaries and more on governance. Key points of contention include the pace of rulemaking for deep-sea mining, environmental risk management, benefit-sharing between developed and developing states, and the influence of early-moving states and contractors over regulatory outcomes. The absence of commercial mining to date has not prevented strategic competition over access and positioning.
Geopolitical Significance: The Area has become a long-term strategic frontier rather than an immediate resource base. States view participation in its governance as a way to secure future access to critical minerals, shape regulatory standards, and influence how global commons are managed. Decisions taken within this framework are likely to have lasting implications for industrial policy, environmental protection, and the credibility of multilateral control over shared spaces.
Malta’s Deep Seabed Initiative
In the late 1960s, advances in deep-sea technology raised concerns that seabed minerals beyond national jurisdiction would be exploited by a small number of technologically advanced states. In 1967, Malta proposed that the deep seabed be placed under international control. The issue became a central point of negotiation during UNCLOS III between 1973 and 1982.
The outcome was agreement that the seabed beyond national jurisdiction would not be subject to national claims and would instead be administered collectively. This led to the designation of the Area as the common heritage of mankind and the creation of the International Seabed Authority.
In Memoriam: The Three Mile Nautical Line
From the 18th century through the early 20th century, many states recognised a three-nautical-mile territorial sea, derived from the so-called cannon shot rule: a state’s sovereignty extended as far as it could defend its coast with shore-based artillery. This informal standard shaped maritime practice during the age of sail and early steam power, providing a narrow belt of coastal control while preserving broad freedom of navigation beyond it.
The rule was never universally codified, and states applied it unevenly as technology advanced. Its gradual erosion reflected growing coastal security concerns and expanding offshore economic interests, setting the stage for wider territorial seas that were later codified under post-war law of the sea frameworks.